diff --git a/mod/assign/feedback/comments/locallib.php b/mod/assign/feedback/comments/locallib.php
index 9ed302ccf83..5c51b004f49 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 57df5a04c86..08a1de15863 100644
--- a/mod/assign/gradingtable.php
+++ b/mod/assign/gradingtable.php
@@ -605,6 +605,9 @@ 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 cceb2d415b7..bf2d4d85bba 100644
--- a/mod/assign/locallib.php
+++ b/mod/assign/locallib.php
@@ -1181,12 +1181,8 @@ 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 {
@@ -1225,9 +1221,6 @@ 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;
@@ -4489,6 +4482,8 @@ 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) {
@@ -4496,7 +4491,9 @@ 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] = $modified;
                         continue;
@@ -4507,6 +4504,8 @@ class assign {
             // Let plugins participate.
             foreach ($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)$modified->lastmodified) {
                             return get_string('errorrecordmodified', 'assign');
@@ -4527,7 +4526,8 @@ class assign {
             if ($current->grade !== null) {
                 $current->grade = floatval($current->grade);
             }
-            if ($current->grade !== $modified->grade) {
+            $gradechanged = $gradecolpresent && $current->grade !== $modified->grade;
+            if ($gradechanged) {
                 // Grade changed.
                 if ($this->grading_disabled($modified->userid)) {
                     continue;
@@ -4551,6 +4551,7 @@ class assign {
             $grade = $this->get_user_grade($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 $plugin) {
@@ -4573,8 +4574,10 @@ class assign {
                 foreach ($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;
                     }
                 }