Index: typo3/sysext/cms/tslib/class.tslib_menu.php
===================================================================
--- typo3/sysext/cms/tslib/class.tslib_menu.php	2009-09-18 15:16:08.000000000 +0200
+++ typo3/sysext/cms/tslib/class.tslib_menu.php	2009-09-18 15:21:32.000000000 +0200
@@ -332,6 +332,15 @@
 			$currentLevel = $startLevel + $this->menuNumber;
 			if (is_array($this->tmpl->rootLine[$currentLevel])) {
 				$nextMParray = $this->MP_array;
+				if (!count($nextMParray) && !$this->tmpl->rootLine[$currentLevel]['_MOUNT_OL'] && $currentLevel > 0) {
+						// Make sure to slide-down any mount point information (_MP_PARAM) to children records in the rootline
+						// otherwise automatic expansion will not work
+					$parentRecord = $this->tmpl->rootLine[$currentLevel - 1];
+					if (isset($parentRecord['_MP_PARAM'])) {
+						$nextMParray[] = $parentRecord['_MP_PARAM'];
+					}
+				}
+				
 				if ($this->tmpl->rootLine[$currentLevel]['_MOUNT_OL']) {	// In overlay mode, add next level MPvars as well:
 					$nextMParray[] = $this->tmpl->rootLine[$currentLevel]['_MP_PARAM'];
 				}