diff --git a/mod/assign/feedback/comments/locallib.php b/mod/assign/feedback/comments/locallib.php
index 96dde23d982..e0ea32e42ab 100644
--- a/mod/assign/feedback/comments/locallib.php
+++ b/mod/assign/feedback/comments/locallib.php
@@ -94,7 +94,10 @@ class assign_feedback_comments extends assign_feedback_plugin {
                 $commenttext = $feedbackcomments->commenttext;
             }
         }
-        return optional_param('quickgrade_comments_' . $userid, '', PARAM_TEXT) != $commenttext;
+        // Note that this handles the difference between empty and not in the quickgrading
+        // form at all (hidden column).
+        $newvalue = optional_param('quickgrade_comments_' . $userid, false, PARAM_TEXT);
+        return ($newvalue !== false) && ($newvalue != $commenttext);
     }
 
 
@@ -173,6 +176,11 @@ class assign_feedback_comments extends assign_feedback_plugin {
     public function save_quickgrading_changes($userid, $grade) {
         global $DB;
         $feedbackcomment = $this->get_feedback_comments($grade->id);
+        $feedbackpresent = optional_param('quickgrade_comments_' . $userid, false, PARAM_TEXT) !== false;
+        if (!$feedbackpresent) {
+            // Nothing to save (e.g. hidden column).
+            return true;
+        }
         if ($feedbackcomment) {
             $feedbackcomment->commenttext = optional_param('quickgrade_comments_' . $userid, '', PARAM_TEXT);
             return $DB->update_record('assignfeedback_comments', $feedbackcomment);
diff --git a/mod/assign/gradingtable.php b/mod/assign/gradingtable.php
index fe5f1e66ce8..c4242511cff 100644
--- a/mod/assign/gradingtable.php
+++ b/mod/assign/gradingtable.php
@@ -759,6 +759,9 @@ class assign_grading_table extends table_sql implements renderable {
                               id="selectuser_' . $row->userid . '"
                               name="selectedusers"
                               value="' . $row->userid . '"/>';
+        $selectcol .= '<input type="hidden"
+                              name="grademodified_' . $row->userid . '"
+                              value="' . $row->timemarked . '"/>';
         return $selectcol;
     }
 
diff --git a/mod/assign/locallib.php b/mod/assign/locallib.php
index fc62b564e74..0ab485fd6b0 100644
--- a/mod/assign/locallib.php
+++ b/mod/assign/locallib.php
@@ -1251,12 +1251,8 @@ class assign {
                               maxlength="10"
                               class="quickgrade"/>';
                 $o .= '&nbsp;/&nbsp;' . format_float($this->get_instance()->grade, 2);
-                $o .= '<input type="hidden"
-                              name="grademodified_' . $userid . '"
-                              value="' . $modified . '"/>';
                 return $o;
             } else {
-                $o .= '<input type="hidden" name="grademodified_' . $userid . '" value="' . $modified . '"/>';
                 if ($grade == -1 || $grade === null) {
                     $o .= '-';
                 } else {
@@ -1295,9 +1291,6 @@ class assign {
                     $o .= '<option value="' . $optionid . '" ' . $selected . '>' . $option . '</option>';
                 }
                 $o .= '</select>';
-                $o .= '<input type="hidden" ' .
-                             'name="grademodified_' . $userid . '" ' .
-                             'value="' . $modified . '"/>';
                 return $o;
             } else {
                 $scaleid = (int)$grade;
@@ -4945,8 +4938,8 @@ class assign {
             $record->userid = $userid;
             if ($modified >= 0) {
                 $record->grade = unformat_float(optional_param('quickgrade_' . $record->userid, -1, PARAM_TEXT));
-                $record->workflowstate = optional_param('quickgrade_' . $record->userid.'_workflowstate', '', PARAM_TEXT);
-                $record->allocatedmarker = optional_param('quickgrade_' . $record->userid.'_allocatedmarker', '', PARAM_INT);
+                $record->workflowstate = optional_param('quickgrade_' . $record->userid.'_workflowstate', false, PARAM_TEXT);
+                $record->allocatedmarker = optional_param('quickgrade_' . $record->userid.'_allocatedmarker', false, PARAM_INT);
             } else {
                 // This user was not in the grading table.
                 continue;
@@ -4984,6 +4977,8 @@ class assign {
         foreach ($currentgrades as $current) {
             $modified = $users[(int)$current->userid];
             $grade = $this->get_user_grade($modified->userid, false);
+            // Check to see if the grade column was even visible.
+            $gradecolpresent = optional_param('quickgrade_' . $modified->userid, false, PARAM_INT) !== false;
 
             // Check to see if the outcomes were modified.
             if ($CFG->enableoutcomes) {
@@ -4991,7 +4986,9 @@ class assign {
                     $oldoutcome = $outcome->grades[$modified->userid]->grade;
                     $paramname = 'outcome_' . $outcomeid . '_' . $modified->userid;
                     $newoutcome = optional_param($paramname, -1, PARAM_FLOAT);
-                    if ($oldoutcome != $newoutcome) {
+                    // Check to see if the outcome column was even visible.
+                    $outcomecolpresent = optional_param($paramname, false, PARAM_FLOAT) !== false;
+                    if ($outcomecolpresent && ($oldoutcome != $newoutcome)) {
                         // Can't check modified time for outcomes because it is not reported.
                         $modifiedusers[$modified->userid] = $modified;
                         continue;
@@ -5002,6 +4999,8 @@ class assign {
             // Let plugins participate.
             foreach ($this->feedbackplugins as $plugin) {
                 if ($plugin->is_visible() && $plugin->is_enabled() && $plugin->supports_quickgrading()) {
+                    // The plugins must handle is_quickgrading_modified correctly - ie
+                    // handle hidden columns.
                     if ($plugin->is_quickgrading_modified($modified->userid, $grade)) {
                         if ((int)$current->lastmodified > (int)$modified->lastmodified) {
                             return get_string('errorrecordmodified', 'assign');
@@ -5022,10 +5021,14 @@ class assign {
             if ($current->grade !== null) {
                 $current->grade = floatval($current->grade);
             }
-            if ($current->grade !== $modified->grade ||
-                 ($this->get_instance()->markingallocation && $current->allocatedmarker != $modified->allocatedmarker ) ||
-                 ($this->get_instance()->markingworkflow && $current->workflowstate !== $modified->workflowstate )) {
-
+            $gradechanged = $gradecolpresent && $current->grade !== $modified->grade;
+            $markingallocationchanged = $this->get_instance()->markingallocation &&
+                                            ($modified->allocatedmarker !== false) &&
+                                            ($current->allocatedmarker != $modified->allocatedmarker);
+            $workflowstatechanged = $this->get_instance()->markingworkflow &&
+                                            ($modified->workflowstate !== false) &&
+                                            ($current->workflowstate != $modified->workflowstate);
+            if ($gradechanged || $markingallocationchanged || $workflowstatechanged) {
                 // Grade changed.
                 if ($this->grading_disabled($modified->userid)) {
                     continue;
@@ -5050,6 +5053,7 @@ class assign {
             $flags = $this->get_user_flags($userid, true);
             $grade->grade= grade_floatval(unformat_float($modified->grade));
             $grade->grader= $USER->id;
+            $gradecolpresent = optional_param('quickgrade_' . $userid, false, PARAM_INT) !== false;
 
             // Save plugins data.
             foreach ($this->feedbackplugins as $plugin) {
@@ -5063,11 +5067,21 @@ class assign {
                 }
             }
 
-            if ($flags->workflowstate != $modified->workflowstate ||
-                $flags->allocatedmarker != $modified->allocatedmarker) {
+            // These will be set to false if they are not present in the quickgrading
+            // form (e.g. column hidden).
+            $workflowstatemodified = ($modified->workflowstate !== false) &&
+                                        ($flags->workflowstate != $modified->workflowstate);
 
+            $allocatedmarkermodified = ($modified->allocatedmarker !== false) &&
+                                        ($flags->allocatedmarker != $modified->allocatedmarker);
+
+            if ($workflowstatemodified) {
                 $flags->workflowstate = $modified->workflowstate;
+            }
+            if ($allocatedmarkermodified) {
                 $flags->allocatedmarker = $modified->allocatedmarker;
+            }
+            if ($workflowstatemodified || $allocatedmarkermodified) {
                 $this->update_user_flags($flags);
             }
             $this->update_grade($grade);
@@ -5082,8 +5096,10 @@ class assign {
                 foreach ($modified->gradinginfo->outcomes as $outcomeid => $outcome) {
                     $oldoutcome = $outcome->grades[$modified->userid]->grade;
                     $paramname = 'outcome_' . $outcomeid . '_' . $modified->userid;
-                    $newoutcome = optional_param($paramname, -1, PARAM_INT);
-                    if ($oldoutcome != $newoutcome) {
+                    // This will be false if the input was not in the quickgrading
+                    // form (e.g. column hidden).
+                    $newoutcome = optional_param($paramname, false, PARAM_INT);
+                    if ($newoutcome !== false && ($oldoutcome != $newoutcome)) {
                         $data[$outcomeid] = $newoutcome;
                     }
                 }