Index: typo3/sysext/cms/tslib/class.tslib_menu.php
===================================================================
--- typo3/sysext/cms/tslib/class.tslib_menu.php	(revision 6485)
+++ typo3/sysext/cms/tslib/class.tslib_menu.php	(working copy)
@@ -2888,10 +2888,6 @@
 			$pid = $mount_info['mount_pid'];
 		}
 
-			// Set "&MP=" var:
-		$MP_var = implode(',',$MP_array);
-		$MP_params = $MP_var ? '&MP='.rawurlencode($MP_var) : '';
-
 			// UIDs to ban:
 		$banUidArray = $this->getBannedUids();
 
@@ -2904,11 +2900,22 @@
 
 		$menuItems = is_array($menuItemArray) ? $menuItemArray : $this->sys_page->getMenu($pid);
 		foreach($menuItems as $uid => $data)	{
+
+			// $data['_MP_PARAM'] contains MP param for overlay mount points (MPs with "substitute this page" set)
+			// if present: add param to copy of MP array (copy used for that submenu branch only)
+			if(array_key_exists('_MP_PARAM', $data) && $data['_MP_PARAM']) {
+				$MP_array[] = $data['_MP_PARAM'];
+			}
+			// Set "&MP=" var:
+			$MP_var = implode(',', $MP_array);
+			$MP_params = $MP_var ? '&MP=' . rawurlencode($MP_var) : '';
+
 			$spacer = (t3lib_div::inList($this->spacerIDList,$data['doktype'])?1:0);		// if item is a spacer, $spacer is set
 			if ($this->mconf['SPC'] || !$spacer)	{	// If the spacer-function is not enabled, spacers will not enter the $menuArr