Index: wp-includes/class-wp-admin-bar.php
===================================================================
--- wp-includes/class-wp-admin-bar.php	(revision 20831)
+++ wp-includes/class-wp-admin-bar.php	(working copy)
@@ -235,11 +235,8 @@
 			// Generate the group class (we distinguish between top level and other level groups).
 			$group_class = ( $node->parent == 'root' ) ? 'ab-top-menu' : 'ab-submenu';
 
-			if ( $node->type == 'group' ) {
-				if ( empty( $node->meta['class'] ) )
-					$node->meta['class'] = '';
-				$node->meta['class'] .= ' ' . $group_class;
-			}
+			if ( $node->type == 'group' )
+				( empty( $node->meta['class'] ) ) ? $node->meta['class'] = $group_class : $node->meta['class'] .= ' ' . $group_class;
 
 			// Items in items aren't allowed. Wrap nested items in 'default' groups.
 			if ( $parent->type == 'item' && $node->type == 'item' ) {
@@ -394,7 +391,7 @@
 		}
 
 		if ( ! empty( $node->meta['class'] ) )
-			$menuclass .= ' ' . $node->meta['class'];
+			( empty( $menuclass ) ) ? $menuclass .= $node->meta['class'] : $menuclass .= ' ' . $node->meta['class'];
 
 		?>