diff --git a/calendar/event.php b/calendar/event.php
index 540fdae92e3..b7c78d64ab9 100644
--- a/calendar/event.php
+++ b/calendar/event.php
@@ -484,15 +484,17 @@
             echo '<div class="header">'.get_string('newevent', 'calendar').$header.'</div>';
 
             if($eventtype == 'select') {
-                $defaultcourse = $SESSION->cal_course_referer;
-                if(isteacheredit($defaultcourse, $USER->id)) {
-                    $defaultgroup = $groupid = 0;
+                $courseid = optional_param('courseid', $SESSION->cal_course_referer, PARAM_INT);
+                if (!$course = get_record('course', 'id', $courseid)) {
+                    error('Incorrect course ID');
                 }
-                else {
-                    $defaultgroup = user_group($defaultcourse, $USER->id);
-                    $groupid      = optional_param('groupid',  $defaultgroup->id, PARAM_INT);
+                if ($groupmode = groupmode($course)) {   // Groups are being used
+                    $changegroup = optional_param('group', -1, PARAM_INT);
+                    $groupid = get_and_set_current_group($course, $groupmode, $changegroup);
+                } else {
+                    $groupid = 0;
                 }
-                $courseid = optional_param('courseid', $defaultcourse, PARAM_INT);
+
                 echo '<h2>'.get_string('eventkind', 'calendar').':</h2>';
                 echo '<div id="selecteventtype">';
                 include('event_select.html');
diff --git a/lib/moodlelib.php b/lib/moodlelib.php
index 739a3fd3fe9..b823c5d8095 100644
--- a/lib/moodlelib.php
+++ b/lib/moodlelib.php
@@ -3646,11 +3646,7 @@ function setup_and_print_groups($course, $groupmode, $urlroot) {
 
     global $USER, $SESSION; //needs his id, need to hack his groups in session
 
-    if (isset($_GET['group'])) {
-        $changegroup = $_GET['group'];  /// 0 or higher
-    } else {
-        $changegroup = -1;              /// This means no group change was specified
-    }
+    $changegroup = optional_param('group', -1, PARAM_INT);
 
     $currentgroup = get_and_set_current_group($course, $groupmode, $changegroup);
     if ($currentgroup === false) {
diff --git a/mod/assignment/lib.php b/mod/assignment/lib.php
index af9008cf30d..20f30925391 100644
--- a/mod/assignment/lib.php
+++ b/mod/assignment/lib.php
@@ -274,7 +274,7 @@ class assignment_base {
         $submitted = '';
 
         if (isteacher($this->course->id)) {
-            if (!isteacheredit($this->course->id) and user_group($this->course->id, $USER->id)) {
+            if (!isteacheredit($this->course->id) and (groupmode($this->course, $this->cm) == SEPARATEGROUPS)) {
                 $count = $this->count_real_submissions($this->currentgroup);  // Only their group
             } else {
                 $count = $this->count_real_submissions();                     // Everyone
@@ -1362,10 +1362,14 @@ class assignment_base {
         $user = get_record('user', 'id', $submission->userid);
 
         if (groupmode($this->course, $this->cm) == SEPARATEGROUPS) {   // Separate groups are being used
-            if (!$group = user_group($this->course->id, $user->id)) {             // Try to find a group
-                $group->id = 0;                                             // Not in a group, never mind
+            if ($groups = user_group($this->course->id, $user->id)) {  // Try to find groups
+                $teachers = array();
+                foreach ($groups as $group) {
+                    $teachers = array_merge($teachers, get_group_teachers($this->course->id, $group->id));
+                }
+            } else {
+                $teachers = get_group_teachers($this->course->id, 0);   // Works even if not in group
             }
-            $teachers = get_group_teachers($this->course->id, $group->id);        // Works even if not in group
         } else {
             $teachers = get_course_teachers($this->course->id);
         }
diff --git a/mod/choice/report.php b/mod/choice/report.php
index 4923e4c57df..8061e13842e 100644
--- a/mod/choice/report.php
+++ b/mod/choice/report.php
@@ -115,9 +115,8 @@
                     $studentid=(!empty($user->idnumber) ? $user->idnumber : " ");
                     $myxls->write_string($row,2,$studentid);
                     $ug2 = '';
-                    $usergrp = user_group($course->id, $user->id);
-                    if (!empty($usergrp)) {
-                        foreach ($usergrp as $ug) {
+                    if ($usergrps = user_group($course->id, $user->id)) {
+                        foreach ($usergrps as $ug) {
 						    $ug2 = $ug2. $ug->name;
 					    }
 			        }
@@ -170,9 +169,8 @@
 		 	  }              
               echo "\t". $studentid."\t";
               $ug2 = '';
-              $usergrp = user_group($course->id, $user->id);
-              if (!empty($usergrp)) {
-                  foreach ($usergrp as $ug) {
+              if ($usergrps = user_group($course->id, $user->id)) {
+                  foreach ($usergrps as $ug) {
 			          $ug2 = $ug2. $ug->name;
 			      }
 			  }
diff --git a/mod/data/lib.php b/mod/data/lib.php
index 6f8be542c0c..7a1edde224e 100755
--- a/mod/data/lib.php
+++ b/mod/data/lib.php
@@ -1175,8 +1175,8 @@ function data_print_comment($data, $comment, $page=0) {
     echo '</div></td></tr>';
 
     echo '<tr><td class="left side">';
-    if ($group = user_group($data->course, $comment->userid)) {
-        print_group_picture($group, $data->course, false, false, true);
+    if ($groups = user_group($data->course, $comment->userid)) {
+        print_group_picture($groups, $data->course, false, false, true);
     } else {
         echo '&nbsp;';
     }