Index: wp-includes/nav-menu-template.php
===================================================================
--- wp-includes/nav-menu-template.php	(revision 16283)
+++ wp-includes/nav-menu-template.php	(working copy)
@@ -313,6 +313,8 @@
 
 	$possible_object_parents = array_filter( $possible_object_parents );
 
+	$front_page_url = home_url();
+
 	foreach ( (array) $menu_items as $key => $menu_item ) {
 
 		$menu_items[$key]->current = false;
@@ -383,6 +385,10 @@
 				$active_parent_item_ids[] = (int) $menu_item->menu_item_parent;
 				$active_parent_object_ids[] = (int) $menu_item->post_parent;
 				$active_object = $menu_item->object;
+
+			// give front page item current-menu-item class when extra query arguments involved
+			} elseif ( $item_url == $front_page_url && is_front_page() ) {
+				$classes[] = 'current-menu-item';
 			}
 
 			if ( untrailingslashit($item_url) == home_url() )
@@ -477,4 +483,4 @@
 	$_used_ids[] = $item->ID;
 	return $id;
 }
-add_filter( 'nav_menu_item_id', '_nav_menu_item_id_use_once', 10, 2 );
\ No newline at end of file
+add_filter( 'nav_menu_item_id', '_nav_menu_item_id_use_once', 10, 2 );