diff --git a/library/Icinga/Web/Controller/ActionController.php b/library/Icinga/Web/Controller/ActionController.php
index 7429d89c8..be0f32756 100644
--- a/library/Icinga/Web/Controller/ActionController.php
+++ b/library/Icinga/Web/Controller/ActionController.php
@@ -160,16 +160,22 @@ class ActionController extends Zend_Controller_Action
      * Return a window-aware session by using the given prefix
      *
      * @param   string      $prefix     The prefix to use
+     * @param   bool        $reset      Whether to reset any existing session-data
      *
      * @return  SessionNamespace
      */
-    public function getWindowSession($prefix)
+    public function getWindowSession($prefix, $reset = false)
     {
         $session = Session::getSession();
         $windowId = $this->getWindowId();
-        $namespace = $session->getNamespace($prefix . '_' . $windowId);
 
-        if ($windowId !== 'undefined' && $session->hasNamespace($prefix . '_undefined')) {
+        $identifier = $prefix . '_' . $windowId;
+        if ($reset && $session->hasNamespace($identifier)) {
+            $session->removeNamespace($identifier);
+        }
+        $namespace = $session->getNamespace($identifier);
+
+        if (!$reset && $windowId !== 'undefined' && $session->hasNamespace($prefix . '_undefined')) {
             // We do not have any window-id on the very first request. Now we add all values from the
             // namespace, that has been created in this case, to the new one and remove it afterwards.
             foreach ($session->getNamespace($prefix . '_undefined') as $name => $value) {
diff --git a/modules/monitoring/application/controllers/TimelineController.php b/modules/monitoring/application/controllers/TimelineController.php
index d7343e054..7bebb6d82 100644
--- a/modules/monitoring/application/controllers/TimelineController.php
+++ b/modules/monitoring/application/controllers/TimelineController.php
@@ -66,7 +66,7 @@ class Monitoring_TimelineController extends ActionController
         $timeline->setMinimumCircleWidth('0.15em');
         $timeline->setDisplayRange($displayRange);
         $timeline->setForecastRange($forecastRange);
-        $timeline->setSession($this->getWindowSession('timeline'));
+        $timeline->setSession($this->getWindowSession('timeline', $this->getRequest()->getParam('extend') != 1));
 
         $this->view->timeline = $timeline;
         $this->view->intervalFormat = $this->getIntervalFormat();
diff --git a/modules/monitoring/library/Monitoring/Timeline/TimeLine.php b/modules/monitoring/library/Monitoring/Timeline/TimeLine.php
index bb2651ea2..88396a43f 100644
--- a/modules/monitoring/library/Monitoring/Timeline/TimeLine.php
+++ b/modules/monitoring/library/Monitoring/Timeline/TimeLine.php
@@ -270,7 +270,6 @@ class TimeLine implements IteratorAggregate
     {
         if ($this->calculationBase === null) {
             if ($this->session !== null) {
-                // TODO: Do not use this if the interval has changed or the user did a reload
                 $this->calculationBase = $this->session->get('calculationBase');
             }