diff --git a/lib/adminlib.php b/lib/adminlib.php
index 86997359dcb..610558c4f1d 100644
--- a/lib/adminlib.php
+++ b/lib/adminlib.php
@@ -5391,7 +5391,7 @@ class admin_setting_manageportfolio extends admin_setting {
 function admin_externalpage_setup($section, $extrabutton = '', array $extraurlparams = null, $actualurl = '') {
     global $CFG, $PAGE, $USER, $SITE, $OUTPUT;
 
-    $PAGE->set_context(get_context_instance(CONTEXT_SYSTEM));
+    $PAGE->set_context(null); // hack - set context to something, by default to system context
 
     $site = get_site();
     require_login();
diff --git a/lib/outputrenderers.php b/lib/outputrenderers.php
index 1dcf3e6136a..c1ef9d2c8e3 100644
--- a/lib/outputrenderers.php
+++ b/lib/outputrenderers.php
@@ -1964,6 +1964,7 @@ EOD;
                 // can not be used from command line or when outputting custom XML
                 @header($_SERVER['SERVER_PROTOCOL'] . ' 404 Not Found');
             }
+            $this->page->set_context(null); // ugly hack - make sure page context is set to something, we do not want bogus warnings here
             $this->page->set_url('/'); // no url
             //$this->page->set_pagelayout('base'); //TODO: MDL-20676 blocks on error pages are weird, unfortunately it somehow detect the pagelayout from URL :-(
             $this->page->set_title(get_string('error'));
@@ -2581,6 +2582,9 @@ class core_renderer_ajax extends core_renderer {
      */
     public function fatal_error($message, $moreinfourl, $link, $backtrace, $debuginfo = null) {
         global $FULLME, $USER;
+
+        $this->page->set_context(null); // ugly hack - make sure page context is set to something, we do not want bogus warnings here
+
         $e = new stdClass();
         $e->error      = $message;
         $e->stacktrace = NULL;
diff --git a/lib/pagelib.php b/lib/pagelib.php
index ec823b21eae..8a16473cf1f 100644
--- a/lib/pagelib.php
+++ b/lib/pagelib.php
@@ -328,12 +328,13 @@ class moodle_page {
      */
     protected function magic_get_context() {
         if (is_null($this->_context)) {
-            if (CLI_SCRIPT) {
-                // cli scripts work in system context, do not annoy devs with fatal errors here
-                $this->_context = get_context_instance(CONTEXT_SYSTEM);
+            if (CLI_SCRIPT or NO_MOODLE_COOKIES) {
+                // cli scripts work in system context, do not annoy devs with debug info
+                // very few scripts do not use cookies, we can safely use system as default context there
             } else {
-                throw new coding_exception('$PAGE->context accessed before it was known.');
+                debugging('Coding problem: this page does not set $PAGE->context properly.');
             }
+            $this->_context = get_context_instance(CONTEXT_SYSTEM);
         }
         return $this->_context;
     }
@@ -641,7 +642,7 @@ class moodle_page {
         if ($this->_legacypageobject) {
             return $this->_legacypageobject->user_allowed_editing();
         }
-        return has_any_capability($this->all_editing_caps(), $this->context);
+        return has_any_capability($this->all_editing_caps(), $this->_context);
     }
 
     /**
@@ -652,7 +653,7 @@ class moodle_page {
         $summary = '';
         $summary .= 'General type: ' . $this->pagelayout . '. ';
         if (!during_initial_install()) {
-            $summary .= 'Context ' . print_context_name($this->context) . ' (context id ' . $this->context->id . '). ';
+            $summary .= 'Context ' . print_context_name($this->_context) . ' (context id ' . $this->_context->id . '). ';
         }
         $summary .= 'Page type ' . $this->pagetype .  '. ';
         if ($this->subpage) {
@@ -723,6 +724,28 @@ class moodle_page {
      * @param object $context a context object, normally obtained with get_context_instance.
      */
     public function set_context($context) {
+        if ($context === null) {
+            // extremely ugly hack which sets context to some value in order to prevent warnings,
+            // use only for core error handling!!!!
+            if (!$this->_context) {
+                $this->_context = get_context_instance(CONTEXT_SYSTEM);
+            }
+            return;
+        }
+
+        // ideally we should set context only once
+        if (isset($this->_context)) {
+            if ($context->id == $this->_context->id) {
+                // fine - no change needed
+            } else if ($this->_context->contextlevel == CONTEXT_SYSTEM or $this->_context->contextlevel == CONTEXT_COURSE) {
+                // hmm - not ideal, but it might produce too many warnings due to the design of require_login
+            } else {
+                // we do not want devs to do weird switching of context levels on the fly,
+                // because we might have used the context already such as in text filter in page title
+                debugging('Coding problem: unsupported modification of PAGE->context from '.$this->_context->contextlevel.' to '.$context->contextlevel);
+            }
+        }
+
         $this->_context = $context;
     }
 
@@ -732,6 +755,8 @@ class moodle_page {
      * @param objcet $cm a full cm object obtained from get_coursemodule_from_id or get_coursemodule_from_instance.
      */
     public function set_cm($cm, $course = null, $module = null) {
+        global $DB;
+
         if (!isset($cm->name) || !isset($cm->modname) || !isset($cm->id)) {
             throw new coding_exception('The $cm you set on $PAGE must have been obtained with get_coursemodule_from_id or get_coursemodule_from_instance. That is, the ->name and -> modname fields must be present and correct.');
         }
@@ -742,8 +767,7 @@ class moodle_page {
         }
         if (!$this->_course || $this->_course->id != $cm->course) {
             if (!$course) {
-                global $DB;
-                $course = $DB->get_record('course', array('id' => $cm->course));
+                $course = $DB->get_record('course', array('id' => $cm->course), '*', MUST_EXIST);
             }
             if ($course->id != $cm->course) {
                 throw new coding_exception('The course you passed to $PAGE->set_cm does not seem to correspond to the $cm.');
@@ -1115,6 +1139,11 @@ class moodle_page {
             return;
         }
 
+        if (!during_initial_install()) {
+            // detect PAGE->context mess
+            $this->magic_get_context();
+        }
+
         if (!$this->_course && !during_initial_install()) {
             $this->set_course($SITE);
         }
@@ -1290,7 +1319,7 @@ class moodle_page {
 
         if (!during_initial_install()) {
             $this->add_body_class('course-' . $this->_course->id);
-            $this->add_body_class('context-' . $this->context->id);
+            $this->add_body_class('context-' . $this->_context->id);
         }
 
         if (!empty($this->_cm)) {
@@ -1669,10 +1698,10 @@ function page_map_class($type, $classname = NULL) {
  * @deprecated since Moodle 2.0
  * Parent class from which all Moodle page classes derive
  *
- * @package   moodlecore
- * @subpackage pages
- * @copyright 1999 onwards Martin Dougiamas  {@link http://moodle.com}
- * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ * @package    core
+ * @subpackage lib
+ * @copyright  1999 onwards Martin Dougiamas  {@link http://moodle.com}
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 class page_base extends moodle_page {
     /**
@@ -1707,10 +1736,10 @@ class page_base extends moodle_page {
  * Although this does nothing, this class declaration should be left for now
  * since there may be legacy class doing class page_... extends page_course
  *
- * @package   moodlecore
- * @subpackage pages
- * @copyright 1999 onwards Martin Dougiamas  {@link http://moodle.com}
- * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ * @package    core
+ * @subpackage lib
+ * @copyright  1999 onwards Martin Dougiamas  {@link http://moodle.com}
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 class page_course extends page_base {
 }
@@ -1719,10 +1748,10 @@ class page_course extends page_base {
  * @deprecated since Moodle 2.0
  * Class that models the common parts of all activity modules
  *
- * @package   moodlecore
- * @subpackage pages
- * @copyright 1999 onwards Martin Dougiamas  {@link http://moodle.com}
- * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ * @package    core
+ * @subpackage lib
+ * @copyright  1999 onwards Martin Dougiamas  {@link http://moodle.com}
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 class page_generic_activity extends page_base {
     // Although this function is deprecated, it should be left here because
diff --git a/lib/setuplib.php b/lib/setuplib.php
index b67cc77128e..106040e34c5 100644
--- a/lib/setuplib.php
+++ b/lib/setuplib.php
@@ -963,18 +963,24 @@ class bootstrap_renderer {
             $recursing = is_early_init($backtrace);
         }
 
+        $earlymethods = array(
+            'fatal_error' => 'early_error',
+            'notification' => 'early_notification',
+        );
+
         // If lib/outputlib.php has been loaded, call it.
         if (!empty($PAGE) && !$recursing) {
+            if (array_key_exists($method, $earlymethods)) {
+                //prevent PAGE->context warnings - exceptions might appear before we set any context
+                $PAGE->set_context(null);
+            }
             $PAGE->initialise_theme_and_output();
             return call_user_func_array(array($OUTPUT, $method), $arguments);
         }
 
         $this->initialising = true;
+
         // Too soon to initialise $OUTPUT, provide a couple of key methods.
-        $earlymethods = array(
-            'fatal_error' => 'early_error',
-            'notification' => 'early_notification',
-        );
         if (array_key_exists($method, $earlymethods)) {
             return call_user_func_array(array('bootstrap_renderer', $earlymethods[$method]), $arguments);
         }