Index: wp-admin/includes/plugin.php
===================================================================
--- wp-admin/includes/plugin.php	(revision 15264)
+++ wp-admin/includes/plugin.php	(working copy)
@@ -1187,7 +1187,10 @@
 
 	if ( isset( $_parent_pages[$menu_slug] ) ) {
 		if ( $_parent_pages[$menu_slug] ) {
-			$url = admin_url($_parent_pages[$menu_slug] . '?page=' . $menu_slug);
+			if ( strpos( $_parent_pages[$menu_slug], '?' ) !== false )
+				$url = admin_url($_parent_pages[$menu_slug] . '&page=' . $menu_slug);
+			else
+				$url = admin_url($_parent_pages[$menu_slug] . '?page=' . $menu_slug);
 		} else {
 			$url = admin_url('admin.php?page=' . $menu_slug);
 		}