Index: wp-includes/class-wp-admin-bar.php
===================================================================
--- wp-includes/class-wp-admin-bar.php	(revision 21078)
+++ wp-includes/class-wp-admin-bar.php	(working copy)
@@ -237,8 +237,9 @@
 
 			if ( $node->type == 'group' ) {
 				if ( empty( $node->meta['class'] ) )
-					$node->meta['class'] = '';
-				$node->meta['class'] .= ' ' . $group_class;
+					$node->meta['class'] = $group_class;
+				else
+					$node->meta['class'] .= ' ' . $group_class;
 			}
 
 			// Items in items aren't allowed. Wrap nested items in 'default' groups.
@@ -389,12 +390,12 @@
 		$aria_attributes = 'tabindex="' . $tabindex . '"';
 
 		if ( $is_parent ) {
-			$menuclass = 'menupop';
+			$menuclass = 'menupop ';
 			$aria_attributes .= ' aria-haspopup="true"';
 		}
 
 		if ( ! empty( $node->meta['class'] ) )
-			$menuclass .= ' ' . $node->meta['class'];
+			$menuclass .= $node->meta['class'];
 
 		?>