Index: branches/RC/core/kernel/application.php
===================================================================
diff -u -r10274 -r10334
--- branches/RC/core/kernel/application.php	(.../application.php)	(revision 10274)
+++ branches/RC/core/kernel/application.php	(.../application.php)	(revision 10334)
@@ -2226,16 +2226,23 @@
 	 * @access public
 	 * @author Kostja / Alex
 	 */
-	function GetTopmostPrefix($current_prefix, $real_top=false)
+	function GetTopmostPrefix($current_prefix, $real_top = false)
 	{
 		// 1. get genealogical tree of $current_prefix
 		$prefixes = Array ($current_prefix);
 		while ( $parent_prefix = $this->getUnitOption($current_prefix, 'ParentPrefix') ) {
+			if (!$this->prefixRegistred($parent_prefix)) {
+				// stop searching, when parent prefix is not registered
+				break;
+			}
+
 			$current_prefix = $parent_prefix;
 			array_unshift($prefixes, $current_prefix);
 		}
 
-		if ($real_top) return $current_prefix;
+		if ($real_top) {
+			return $current_prefix;
+		}
 
 		// 2. find what if parent is passed
 		$passed = explode(',', $this->GetVar('all_passed'));