diff --git a/blocks/calendar_month/block_calendar_month.php b/blocks/calendar_month/block_calendar_month.php
index 9fa7ecb..f1de52d 100644
--- a/blocks/calendar_month/block_calendar_month.php
+++ b/blocks/calendar_month/block_calendar_month.php
@@ -36,7 +36,8 @@ class block_calendar_month extends block_base {
             // the list of courses it will be grabbing events from.
             $filtercourse    = NULL;
             $groupeventsfrom = NULL;
-            $SESSION->cal_courses_shown = calendar_get_default_courses(true);
+            $SESSION->cal_courses_shown = 0; //calendar_get_default_courses(true);
+            $coursesshown = calendar_get_default_courses(true);
             calendar_set_referring_course(0);
 
         } else {
@@ -49,9 +50,9 @@ class block_calendar_month extends block_base {
         calendar_set_referring_course($courseshown);
 
         // MDL-9059, set to show this course when admins go into a course, then unset it.
-        if ($this->page->course->id != SITEID && !isset($SESSION->cal_courses_shown[$this->page->course->id]) && has_capability('moodle/calendar:manageentries', get_context_instance(CONTEXT_SYSTEM))) {
+        if ($this->page->course->id != SITEID && !isset($coursesshown[$this->page->course->id]) && has_capability('moodle/calendar:manageentries', get_context_instance(CONTEXT_SYSTEM))) {
             $courseset = true;
-            $SESSION->cal_courses_shown[$this->page->course->id] = $this->page->course;
+            $coursesshown[$this->page->course->id] = $this->page->course;
         }
 
         // Be VERY careful with the format for default courses arguments!
@@ -73,9 +74,9 @@ class block_calendar_month extends block_base {
         }
 
         // MDL-9059, unset this so that it doesn't stay in session
-        if (!empty($courseset)) {
-            unset($SESSION->cal_courses_shown[$this->page->course->id]);
-        }
+        //if (!empty($courseset)) {
+        //    unset($SESSION->cal_courses_shown[$this->page->course->id]);
+        //}
 
         return $this->content;
     }
diff --git a/blocks/calendar_upcoming/block_calendar_upcoming.php b/blocks/calendar_upcoming/block_calendar_upcoming.php
index 21d63b4..ff289e0 100644
--- a/blocks/calendar_upcoming/block_calendar_upcoming.php
+++ b/blocks/calendar_upcoming/block_calendar_upcoming.php
@@ -42,7 +42,7 @@ class block_calendar_upcoming extends block_base {
                 // the list of courses it will be grabbing events from.
                 $filtercourse    = NULL;
                 $groupeventsfrom = NULL;
-                $SESSION->cal_courses_shown = calendar_get_default_courses(true);
+                $SESSION->cal_courses_shown = 0; //calendar_get_default_courses(true);
                 calendar_set_referring_course(0);
             } else {
                 // Forcibly filter events to include only those from the particular course we are in.
diff --git a/calendar/event.php b/calendar/event.php
index f2fa293..430d875 100644
--- a/calendar/event.php
+++ b/calendar/event.php
@@ -104,7 +104,7 @@ $courseexists = false;
 if ($courseid > 0) {
     if ($courseid == SITEID) {
         // If coming from the site page, show all courses
-        $SESSION->cal_courses_shown = calendar_get_default_courses(true);
+        $SESSION->cal_courses_shown = 0; //calendar_get_default_courses(true);
         calendar_set_referring_course(0);
     } else if ($DB->record_exists('course', array('id'=>$courseid))) {
         $courseexists = true;
diff --git a/calendar/lib.php b/calendar/lib.php
index 4917100..88f360c 100644
--- a/calendar/lib.php
+++ b/calendar/lib.php
@@ -1227,9 +1227,9 @@ function calendar_session_vars($course=null) {
             $course = clone $course;
             unset($course->coursenode);
         }
-        $SESSION->cal_courses_shown = array($course->id => $course);
+        $SESSION->cal_courses_shown = $course->id;
     } else {
-        $SESSION->cal_courses_shown = calendar_get_default_courses(true);
+        $SESSION->cal_courses_shown = 0; //calendar_get_default_courses(true);
     }
     if(empty($SESSION->cal_users_shown)) {
         // The empty() instead of !isset() here makes a whole world of difference,
@@ -1253,11 +1253,11 @@ function calendar_set_filters(&$courses, &$group, &$user, $courseeventsfrom = NU
     // Insidious bug-wannabe: setting $SESSION->cal_courses_shown to $course->id would cause
     // the code to function incorrectly UNLESS we convert it to an integer. One case where
     // PHP's loose type system works against us.
-    if(is_string($SESSION->cal_courses_shown)) {
+    if(is_string($SESSION->cal_courses_shown) && $SESSION->cal_courses_shown > 0) {
         $SESSION->cal_courses_shown = intval($SESSION->cal_courses_shown);
     }
     if($courseeventsfrom === NULL) {
-        $courseeventsfrom = $SESSION->cal_courses_shown;
+        $courseeventsfrom = ($SESSION->cal_courses_shown === 0 ? calendar_get_default_courses(true) : $SESSION->cal_courses_shown);
     }
 
     // MDL-9059, $courseeventsfrom can be an int, or an array of ints, or an array of course objects
@@ -1276,7 +1276,7 @@ function calendar_set_filters(&$courses, &$group, &$user, $courseeventsfrom = NU
     }
 
     if($groupeventsfrom === NULL) {
-        $groupeventsfrom = $SESSION->cal_courses_shown;
+        $groupeventsfrom = ($SESSION->cal_courses_shown === 0 ? calendar_get_default_courses(true) : $SESSION->cal_courses_shown);
     }
 
     if(($SESSION->cal_show_course && $SESSION->cal_show_global) || $ignorefilters) {
@@ -1369,7 +1369,7 @@ function calendar_set_filters(&$courses, &$group, &$user, $courseeventsfrom = NU
                             $groupids[] = $courseid;
                         }
                     }
-                    else if(isset($SESSION->cal_courses_shown[$courseid]) && ($SESSION->cal_courses_shown[$courseid]->groupmode != NOGROUPS || !$SESSION->cal_courses_shown[$courseid]->groupmodeforce)) {
+                    else if(isset($courseeventsfrom[$courseid]) && ($courseeventsfrom[$courseid]->groupmode != NOGROUPS || !$courseeventsfrom[$courseid]->groupmodeforce)) {
                         $groupids[] = $courseid;
                     }
                 }
diff --git a/calendar/renderer.php b/calendar/renderer.php
index 1c906d6..513685e 100644
--- a/calendar/renderer.php
+++ b/calendar/renderer.php
@@ -650,7 +650,7 @@ class core_calendar_renderer extends plugin_renderer_base {
             $courseoptions[$course->id] = format_string($course->shortname);
         }
 
-        if (is_numeric($SESSION->cal_courses_shown)) {
+        if (is_numeric($SESSION->cal_courses_shown) && $SESSION->cal_courses_shown > 0) {
             $selected = $SESSION->cal_courses_shown;
         } else {
             $selected = '';
@@ -663,4 +663,4 @@ class core_calendar_renderer extends plugin_renderer_base {
         }
         return $this->output->render($select);
     }
-}
\ No newline at end of file
+}
diff --git a/calendar/set.php b/calendar/set.php
index 039139e..8728dbc 100644
--- a/calendar/set.php
+++ b/calendar/set.php
@@ -93,7 +93,7 @@ switch($var) {
             calendar_set_referring_course(0);
         }
         else if($id == 1) {
-            $SESSION->cal_courses_shown = calendar_get_default_courses(true);
+            $SESSION->cal_courses_shown = 0; //calendar_get_default_courses(true);
             calendar_set_referring_course(0);
         }
         else {
@@ -144,4 +144,4 @@ switch($from) {
     break;
     default:
 
-}
\ No newline at end of file
+}
diff --git a/calendar/view.php b/calendar/view.php
index a1a06be..6201153 100644
--- a/calendar/view.php
+++ b/calendar/view.php
@@ -122,7 +122,7 @@ if (!empty($courseid)) {
     if ($course = $DB->get_record('course', array('id'=>$courseid))) {
         if ($course->id == SITEID) {
             // If coming from the home page, show all courses
-            $SESSION->cal_courses_shown = calendar_get_default_courses(true);
+            $SESSION->cal_courses_shown = 0; //calendar_get_default_courses(true);
             calendar_set_referring_course(0);
 
         } else {