diff --git a/phpgwapi/inc/class.egw_framework.inc.php b/phpgwapi/inc/class.egw_framework.inc.php
index 848daca3d0..554816fd23 100644
--- a/phpgwapi/inc/class.egw_framework.inc.php
+++ b/phpgwapi/inc/class.egw_framework.inc.php
@@ -2206,7 +2206,14 @@ if ($app == 'home') continue;
 	public static function ajax_set_preference($app, $name, $value)
 	{
 		$GLOBALS['egw']->preferences->read_repository();
-		$GLOBALS['egw']->preferences->add($app, $name, $value);
+		if ((string)$value === '')
+		{
+			$GLOBALS['egw']->preferences->delete($app, $name);
+		}
+		else
+		{
+			$GLOBALS['egw']->preferences->add($app, $name, $value);
+		}
 		$GLOBALS['egw']->preferences->save_repository(True);
 	}
 
diff --git a/phpgwapi/js/jsapi/egw_preferences.js b/phpgwapi/js/jsapi/egw_preferences.js
index 2f31573f2b..47cebecb11 100644
--- a/phpgwapi/js/jsapi/egw_preferences.js
+++ b/phpgwapi/js/jsapi/egw_preferences.js
@@ -78,15 +78,28 @@ egw.extend('preferences', egw.MODULE_GLOBAL, function() {
 		 *
 		 * @param {string} _app application name or "common"
 		 * @param {string} _name name of the pref
-		 * @param {string} _val value of the pref
+		 * @param {string} _val value of the pref, null, undefined or "" to unset it
 		 * @param {function} _callback Function passed along to the queue, called after preference is set server-side
 		 */
 		set_preference: function(_app, _name, _val, _callback)
 		{
+			// if there is no change, no need to submit it to server
+			if (typeof prefs[_app] != 'undefined' && prefs[_app][_name] === _val) return;
+
 			this.jsonq('home.egw_framework.ajax_set_preference.template',[_app, _name, _val], _callback);
 
 			// update own preference cache, if _app prefs are loaded (dont update otherwise, as it would block loading of other _app prefs!)
-			if (typeof prefs[_app] != 'undefined') prefs[_app][_name] = _val;
+			if (typeof prefs[_app] != 'undefined')
+			{
+				if (_val === undefined || _val === "" || _val === null)
+				{
+					delete prefs[_app][_name];
+				}
+				else
+				{
+					prefs[_app][_name] = _val;
+				}
+			}
 		},
 
 		/**