diff --git a/phpgwapi/js/jsapi/app_base.js b/phpgwapi/js/jsapi/app_base.js
index 30268ef1b2..0ff7045d14 100644
--- a/phpgwapi/js/jsapi/app_base.js
+++ b/phpgwapi/js/jsapi/app_base.js
@@ -100,6 +100,8 @@ var AppJS = Class.extend(
 	 */
 	destroy: function() {
 		delete this.et2;
+		if (this.sidebox)
+			this.sidebox.off();
 		delete this.sidebox;
 		delete window.app[this.appname];
 	},
diff --git a/phpgwapi/js/jsapi/egw_core.js b/phpgwapi/js/jsapi/egw_core.js
index 16016c9e87..1758b2e438 100644
--- a/phpgwapi/js/jsapi/egw_core.js
+++ b/phpgwapi/js/jsapi/egw_core.js
@@ -118,7 +118,7 @@
 	 * @param _moduleInstances is the the object which contains the application
 	 * 	and window specific module instances.
 	 * @param _instances refers to all api instances.
-	 * @param _wnd is the window for which the module instances should get
+	 * @param _window is the window for which the module instances should get
 	 * 	created.
 	 */
 	function getWndModules(_egw, _modules, _moduleInstances, _instances, _window)
@@ -139,8 +139,9 @@
 		// called, we have to delete the module slot created above
 		var fnct = function() {
 			cleanupEgwInstances(_instances, _moduleInstances, function(_w) {
-				return _w.window === _window});
-			};
+				return _w.window === _window;
+			});
+		};
 		if (_window.attachEvent)
 		{
 			_window.attachEvent('onbeforeunload', fnct);
@@ -259,7 +260,7 @@
 		if (typeof _instances[hash] === 'undefined')
 		{
 			_instances[hash] = [];
-			return createEgwInstance(_egw, _modules, _moduleInstances, 
+			return createEgwInstance(_egw, _modules, _moduleInstances,
 				_instances[hash], _instances, _app, _window);
 		}
 		else
@@ -277,7 +278,7 @@
 
 		// If we're still here, no API instance for the given window has been
 		// found -- create a new entry
-		return createEgwInstance(_egw, _modules, _moduleInstances, 
+		return createEgwInstance(_egw, _modules, _moduleInstances,
 			_instances[hash], _instances, _app, _window);
 	}
 
@@ -403,7 +404,7 @@
 			'app': {},
 			'wnd': [],
 			'glo': {}
-		}
+		};
 
 		/**
 		 * instances contains references to all created instances.
@@ -416,7 +417,13 @@
 		 */
 		window.setInterval(function() {
 			cleanupEgwInstances(instances, moduleInstances, function(w) {
-				return w.window && w.window.closed
+				try {
+					return w.window && w.window.closed;
+				}
+				catch(e) {
+					// IE(11) seems to throw a permission denied error, when accessing closed property
+					return true;
+				}
 			});
 		}, 10000);
 
diff --git a/phpgwapi/js/jsapi/egw_debug.js b/phpgwapi/js/jsapi/egw_debug.js
index e4024a7b8a..827f7f47bc 100644
--- a/phpgwapi/js/jsapi/egw_debug.js
+++ b/phpgwapi/js/jsapi/egw_debug.js
@@ -283,8 +283,16 @@ egw.extend('debug', egw.MODULE_GLOBAL, function(_app, _wnd) {
 	// bind to global error handler
 	jQuery(_wnd).on('error', function(e)
 	{
-		// originalEvent does NOT exist in IE
+		// originalEvent does NOT always exist in IE
 		var event = typeof e.originalEvent == 'object' ? e.originalEvent : e;
+		// IE(11) gives a syntaxerror on each pageload pointing to first line of html page (doctype).
+		// As I cant figure out what's wrong there, we are ignoring it for now.
+		if (navigator.userAgent.match(/Trident/i) && typeof event.name == 'undefined' &&
+			Object.prototype.toString.call(event) == '[object ErrorEvent]' &&
+			event.lineno == 1 && event.filename.indexOf('/index.php') != -1)
+		{
+			return false;
+		}
 		log_on_client('error', [event.message], typeof event.stack != 'undefined' ? event.stack : null);
 		raise_error();
 		// rethrow error to let browser log and show it in usual way too