diff --git a/stack/maxima/stackmaxima.mac b/stack/maxima/stackmaxima.mac
index 286d1269d5729c92f0a786d91f4eabe242144d1e..ceee340430b26d5052d562398f9bdfd2a5d0e3bc 100644
--- a/stack/maxima/stackmaxima.mac
+++ b/stack/maxima/stackmaxima.mac
@@ -784,9 +784,6 @@ stack_disp_sub_script(ex) := block([s],
  if taylorp(ex) then return(ex),
  if safe_setp(ex) then return(apply(set, maplist(stack_disp_sub_script, args(ex)))),
  if arrayp(ex) then return(arraymake(op(ex), maplist(stack_disp_sub_script, args(ex)))),
- /* The following are not, strictly speaking, a subscript issue, but we don't want another recursive call. */
- /* Strip out empty plus operators, which cause problems in display with simp:false.             */
- if is(safe_op(ex)="+") and is(length(args(ex))=1) then return(stack_disp_sub_script(first(args(ex)))),
  /* Now deal with supscripts. */
  if not(atom(ex)) then return(apply(op(ex), maplist(stack_disp_sub_script, args(ex)))),
  if simp_numberp(ex) or stringp(ex) or ex or not(ex) then return(ex),
diff --git a/tests/fixtures/inputfixtures.class.php b/tests/fixtures/inputfixtures.class.php
index 49aafc5f4acdfabaccdf8467309fab170c359886..c3cfb3ef30f542a2d82a725e961d837dc7d0347d 100644
--- a/tests/fixtures/inputfixtures.class.php
+++ b/tests/fixtures/inputfixtures.class.php
@@ -408,19 +408,22 @@ class stack_inputvalidation_test_data {
         ],
         ['ycos(2)', 'php_true', 'y*cos(2)', 'cas_true', 'y\cdot \cos \left( 2 \right)', 'missing_stars', ""],
         ['Bgcd(3,2)', 'php_true', 'B*gcd(3,2)', 'cas_true', 'B\cdot 1', 'missing_stars', ""],
-        ['+1', 'php_true', '+1', 'cas_true', '1', '', "Unary plus"],
-        ['+0.200', 'php_true', '+dispdp(0.200,3)', 'cas_true', '0.200', '', ""],
-        ['+e', 'php_true', '+e', 'cas_true', 'e', '', ""],
-        ['+pi', 'php_true', '+pi', 'cas_true', '\pi', '', ""],
-        ['+i', 'php_true', '+i', 'cas_true', '\mathrm{i}', '', ""],
-        ['+x', 'php_true', '+x', 'cas_true', 'x', '', ""],
-        ['sqrt(+x)', 'php_true', 'sqrt(+x)', 'cas_true', '\sqrt{x}', '', ""],
+        ['+1', 'php_true', '+1', 'cas_true', '+1', '', "Unary plus"],
+        // Note: no + in front of the LaTeX below.
+        ['+0.200', 'php_true', '+dispdp(0.200,3)', 'cas_true', '+0.200', '', ""],
+        ['+e', 'php_true', '+e', 'cas_true', '+e', '', ""],
+        ['+pi', 'php_true', '+pi', 'cas_true', '+\pi', '', ""],
+        ['+i', 'php_true', '+i', 'cas_true', '+\mathrm{i}', '', ""],
+        ['+x', 'php_true', '+x', 'cas_true', '+x', '', ""],
+        // The example below is an "odd" output from Maxima.
+        ['sqrt(+x)', 'php_true', 'sqrt(+x)', 'cas_true', '+\sqrt{x}', '', ""],
         ['sqrt(x)^3', 'php_true', 'sqrt(x)^3', 'cas_true', '{\sqrt{x}}^3', '', ""],
-        ['1/sin(+x)', 'php_true', '1/sin(+x)', 'cas_true', '\frac{1}{\sin \left( x \right)}', '', ""],
+        // The example below is an "odd" output from Maxima. I'm not planning to fix this!
+        ['1/sin(+x)', 'php_true', '1/sin(+x)', 'cas_true', '\frac{1+}{\sin \left( x \right)}', '', ""],
         ['"+"(a,b)', 'php_true', '"+"(a,b)', 'cas_true', 'a+b', '', "This is Maxima specific syntax."],
-        ['(+1)', 'php_true', '(+1)', 'cas_true', '1', '', ""],
-        ['[1,+2]', 'php_true', '[1,+2]', 'cas_true', '\left[ 1 , 2 \right]', '', ""],
-        ['[+1,+2]', 'php_true', '[+1,+2]', 'cas_true', '\left[ 1 , 2 \right]', '', ""],
+        ['(+1)', 'php_true', '(+1)', 'cas_true', '+1', '', ""],
+        ['[1,+2]', 'php_true', '[1,+2]', 'cas_true', '\left[ 1 , +2 \right]', '', ""],
+        ['[+1,+2]', 'php_true', '[+1,+2]', 'cas_true', '\left[ +1 , +2 \right]', '', ""],
         ['-1', 'php_true', '-1', 'cas_true', '-1', '', "Unary minus"],
         ['-0.200', 'php_true', '-dispdp(0.200,3)', 'cas_true', '-0.200', '', ""],
         ['-e', 'php_true', '-e', 'cas_true', '-e', '', ""],
@@ -444,7 +447,7 @@ class stack_inputvalidation_test_data {
             '\frac{{-b \pm \sqrt{b^2}}}{2\cdot a}', '', "",
         ],
         ['a+-b', 'php_true', 'a+-b', 'cas_true', '{a \pm b}', '', ""],
-        ['a-+b', 'php_true', 'a-+b', 'cas_true', 'a-b', '', ""],
+        ['a-+b', 'php_true', 'a-+b', 'cas_true', 'a+-\left(b\right)', '', ""],
         ['x & y', 'php_false', 'x & y', '', '', 'spuriousop', "Synonyms"],
         ['x && y', 'php_false', 'x && y', '', '', 'spuriousop', ""],
         ['x and y', 'php_true', 'x and y', 'cas_true', 'x\,{\text{ and }}\, y', '', ""],
@@ -645,10 +648,10 @@ class stack_inputvalidation_test_data {
             '\frac{\ln \left( 2\cdot x \right)}{x}+\frac{1}{2}', 'missing_stars', "",
         ],
         [
-            'a++b', 'php_true', 'a++b', 'cas_true', 'a+b', '',
+            'a++b', 'php_true', 'a++b', 'cas_true', 'a++\left(b\right)', '',
             "The extra plusses or minuses are interpreted as unary operators on b",
         ],
-        ['a +++ b', 'php_true', 'a+++b', 'cas_true', 'a+b', '', ""],
+        ['a +++ b', 'php_true', 'a+++b', 'cas_true', 'a+++\left(\left(b\right)\right)', '', ""],
         ['a --- b', 'php_true', 'a---b', 'cas_true', 'a-\left(-\left(-b\right)\right)', '', ""],
         [
             'rho*z*V/(4*pi*epsilon[0]*(R^2+z^2)^(3/2))', 'php_true', 'rho*z*V/(4*pi*epsilon[0]*(R^2+z^2)^(3/2))', 'cas_true',
diff --git a/tests/helper.php b/tests/helper.php
index 34c780e9f07957220b4e68128fb54a4724661bc0..d28a605af4ba7233624f5aa91b902f09697dfd48 100644
--- a/tests/helper.php
+++ b/tests/helper.php
@@ -73,6 +73,7 @@ class qtype_stack_test_helper extends question_test_helper {
             'validator',          // Test teacher-defined input validators and language.
             'feedback',           // Test teacher-defined input feedback and complex numbers.
             'ordergreat',         // Test the ordergreat function at the question level, e.g. keyvals.
+            'exdowncase',         // Test the ordergreat function with exdowncase.
             // Test questions for all the various input types.
             'algebraic_input',
             'algebraic_input_right',
@@ -4096,6 +4097,94 @@ class qtype_stack_test_helper extends question_test_helper {
         return $q;
     }
 
+    /**
+     * @return qtype_stack_question.
+     */
+    public static function make_stack_question_exdowncase() {
+        $q = self::make_a_stack_question();
+
+        $q->name = 'exdowncase';
+        $q->questionvariables = "ordergreat(x);\nveq: 5*y^2-8*x*y+13*x^2 = 49;";
+        $q->questiontext = "What is {@veq@}? [[input:ansq]][[validation:ansq]]";
+        $q->generalfeedback = '';
+        $q->questionnote = '';
+
+        $q->specificfeedback = '[[feedback:firsttree]]';
+        $q->penalty = 0.25; // Non-zero and not the default.
+
+        $q->inputs['ansq'] = stack_input_factory::make(
+            'algebraic', 'ansq', 'veq', null,
+            [
+                'boxWidth' => 20, 'forbidWords' => ''
+            ]);
+
+        // By setting simp:true (the default) we check the re-ordering really happens.
+        $q->options->set_option('simplify', true);
+
+        $prt = new stdClass;
+        $prt->name              = 'firsttree';
+        $prt->id                = 0;
+        $prt->value             = 1;
+        $prt->feedbackstyle     = 1;
+        $prt->feedbackvariables = 'loweranseq:exdowncase(ansq);';
+        $prt->firstnodename     = '0';
+        $prt->nodes             = [];
+        $prt->autosimplify      = true;
+
+        $newnode = new stdClass;
+        $newnode->id                  = '0';
+        $newnode->nodename            = '0';
+        $newnode->description         = 'Use CasEqual as the test';
+        $newnode->sans                = 'loweranseq';
+        $newnode->tans                = 'veq';
+        $newnode->answertest          = 'CasEqual';
+        $newnode->testoptions         = '';
+        $newnode->quiet               = false;
+        $newnode->falsescore          = '0';
+        $newnode->falsescoremode      = '=';
+        $newnode->falsepenalty        = $q->penalty;
+        $newnode->falsefeedback       = "";
+        $newnode->falsefeedbackformat = '1';
+        $newnode->falseanswernote     = 'firsttree-0-0';
+        $newnode->falsenextnode       = '1';
+        $newnode->truescore           = '1';
+        $newnode->truescoremode       = '=';
+        $newnode->truepenalty         = $q->penalty;
+        $newnode->truefeedback        = "";
+        $newnode->truefeedbackformat  = '1';
+        $newnode->trueanswernote      = 'firsttree-0-1';
+        $newnode->truenextnode        = '1';
+        $prt->nodes[] = $newnode;
+        $newnode = new stdClass;
+        $newnode->id                  = '1';
+        $newnode->nodename            = '1';
+        $newnode->description         = 'Use AlgEquiv as the test';
+        $newnode->sans                = 'loweranseq';
+        $newnode->tans                = 'veq';
+        $newnode->answertest          = 'AlgEquiv';
+        $newnode->testoptions         = '';
+        $newnode->quiet               = false;
+        $newnode->falsescore          = '0';
+        $newnode->falsescoremode      = '=';
+        $newnode->falsepenalty        = $q->penalty;
+        $newnode->falsefeedback       = "";
+        $newnode->falsefeedbackformat = '1';
+        $newnode->falseanswernote     = 'firsttree-1-0';
+        $newnode->falsenextnode       = '-1';
+        $newnode->truescore           = '1';
+        $newnode->truescoremode       = '=';
+        $newnode->truepenalty         = $q->penalty;
+        $newnode->truefeedback        = "";
+        $newnode->truefeedbackformat  = '1';
+        $newnode->trueanswernote      = 'firsttree-1-1';
+        $newnode->truenextnode        = '-1';
+        $prt->nodes[] = $newnode;
+
+        $q->prts[$prt->name] = new stack_potentialresponse_tree_lite($prt, $prt->value, $q);
+
+        return $q;
+    }
+
     /**
      * Make the data what would be received from the editing form for an algebraic input question.
      *
diff --git a/tests/input_algebraic_test.php b/tests/input_algebraic_test.php
index 2a1bb3280f98196cfb14639f2a362be15934c2ad..30fc718b2c749c5e56fb8ab68d34301a111e6558 100644
--- a/tests/input_algebraic_test.php
+++ b/tests/input_algebraic_test.php
@@ -460,7 +460,8 @@ class input_algebraic_test extends qtype_stack_testcase {
                 new stack_cas_security(false, '', '', ['ta']));
         $this->assertEquals(stack_input::VALID, $state->status);
         $this->assertEquals('2*sqrt(+2)/3', $state->contentsmodified);
-        $this->assertEquals('\[ \frac{2\cdot \sqrt{2}}{3} \]', $state->contentsdisplayed);
+        // Maxima's TeX code pulls out the + to outside the sqrt. Known edge case.
+        $this->assertEquals('\[ \frac{2\cdot +\sqrt{2}}{3} \]', $state->contentsdisplayed);
         $this->assertEquals('The answer <span class="filter_mathjaxloader_equation">'
             . '<span class="nolink">\( \frac{2\cdot \sqrt{2}}{3} \)</span></span>, which can be typed as '
             . '<code>2*sqrt(2)/3</code>, would be correct.',
diff --git a/tests/walkthrough_adaptive_test.php b/tests/walkthrough_adaptive_test.php
index f9663e83bc039ca6765af452db5a9491b09fd67b..7bef19bec6345763593b3c27c974c374d00fbccb 100644
--- a/tests/walkthrough_adaptive_test.php
+++ b/tests/walkthrough_adaptive_test.php
@@ -4807,7 +4807,7 @@ class walkthrough_adaptive_test extends qtype_stack_walkthrough_test_base {
         $this->process_submission(['ansq' => $ia, 'ansq_val' => $ia, '-submit' => 1]);
         $this->render();
         $this->assert_content_with_maths_contains('\[ 5\cdot y+3\cdot x=1', $this->currentoutput);
-        $expected = 'Seed: 1; ansq: 5*y+3*x=1 [score]; firsttree: # = 0 | ATCASEqual (AlgEquiv-true)ATEquation_sides.' .
+        $expected = 'Seed: 1; ansq: 5*y+3*x=1 [score]; firsttree: # = 0 | ATCASEqual (AlgEquiv-true)ATEquation_sides. ' .
             '| firsttree-0-0';
         $this->check_response_summary($expected);
 
@@ -4818,4 +4818,73 @@ class walkthrough_adaptive_test extends qtype_stack_walkthrough_test_base {
         $expected = 'Seed: 1; ansq: 3*x+5*y=1 [score]; firsttree: # = 1 | ATCASEqual_true. | firsttree-0-1';
         $this->check_response_summary($expected);
     }
+
+    public function test_input_validator_exdowncase() {
+        $q = test_question_maker::make_question('stack', 'exdowncase');
+        $this->start_attempt_at_question($q, 'adaptive', 1);
+
+        // Check the initial state.
+        $this->check_current_state(question_state::$todo);
+        $this->check_current_mark(null);
+        $this->check_prt_score('firsttree', null, null);
+        $this->render();
+        $this->check_output_contains_text_input('ansq');
+        $this->check_output_does_not_contain_input_validation();
+        $this->check_output_does_not_contain_prt_feedback();
+        $this->check_output_does_not_contain_stray_placeholders();
+        $this->check_current_output(
+            new question_pattern_expectation('/What is/'),
+            $this->get_does_not_contain_feedback_expectation(),
+            $this->get_does_not_contain_num_parts_correct(),
+            $this->get_no_hint_visible_expectation()
+            );
+        $this->assert_content_with_maths_contains('\({13\cdot x^2-8\cdot y\cdot x+5\cdot y^2=49}\)',
+            $this->currentoutput);
+
+        // Process a validate request.
+        $ia = '13*x^2-8*y*x+5*y^2 = 49';
+        $this->process_submission(['ansq' => $ia, '-submit' => 1]);
+
+        $this->check_current_mark(null);
+        $this->check_prt_score('firsttree', null, null);
+        $this->render();
+
+        // Check order of variables in validation of answer matches what students type.
+        $expected = 'Seed: 1; ansq: 13*x^2-8*y*x+5*y^2 = 49 [valid]; firsttree: !';
+        $this->check_response_summary($expected);
+        $this->check_output_contains_text_input('ansq', $ia);
+        $this->check_output_contains_input_validation('ansq');
+        $this->check_output_does_not_contain_prt_feedback();
+        $this->check_output_does_not_contain_stray_placeholders();
+        $this->assert_content_with_maths_contains('\[ 13\cdot x^2-8\cdot y\cdot x+5\cdot y^2=49',
+            $this->currentoutput);
+        $ia = '13*x^2-8*y*x+5*y^2 = 49';
+        $this->process_submission(['ansq' => $ia, 'ansq_val' => $ia, '-submit' => 1]);
+        $this->render();
+        $this->assert_content_with_maths_contains('\[ 13\cdot x^2-8\cdot y\cdot x+5\cdot y^2=49',
+            $this->currentoutput);
+        $expected = 'Seed: 1; ansq: 13*x^2-8*y*x+5*y^2 = 49 [score]; firsttree: # = 1 | ' .
+            'ATCASEqual_true. | firsttree-0-1 | ATEquation_sides | firsttree-1-1';
+        $this->check_response_summary($expected);
+
+        // New answer with upper case.
+        $ia = '13*X^2-8*y*x+5*y^2 = 49';
+        $this->process_submission(['ansq' => $ia, 'ansq_val' => $ia, '-submit' => 1]);
+        $this->render();
+        $this->assert_content_with_maths_contains('\[ 13\cdot X^2-8\cdot y\cdot x+5\cdot y^2=49',
+            $this->currentoutput);
+        $expected = 'Seed: 1; ansq: 13*X^2-8*y*x+5*y^2 = 49 [score]; firsttree: # = 1 | ' .
+            'ATCASEqual_true. | firsttree-0-1 | ATEquation_sides | firsttree-1-1';
+        $this->check_response_summary($expected);
+
+        // New answer which is wrong.
+        $ia = '13*X^2-8*y*x+5*y^2 = 48';
+        $this->process_submission(['ansq' => $ia, 'ansq_val' => $ia, '-submit' => 1]);
+        $this->render();
+        $this->assert_content_with_maths_contains('\[ 13\cdot X^2-8\cdot y\cdot x+5\cdot y^2=48',
+            $this->currentoutput);
+        $expected = 'Seed: 1; ansq: 13*X^2-8*y*x+5*y^2 = 48 [score]; firsttree: # = 0 | ' .
+            'ATCASEqual_false. | firsttree-0-0 | ATEquation_lhs_notrhs | firsttree-1-0';
+        $this->check_response_summary($expected);
+    }
 }