Index: menu-header.php
===================================================================
--- menu-header.php	(revision 36373)
+++ menu-header.php	(working copy)
@@ -76,6 +76,7 @@
 		$aria_attributes = '';
 		$aria_hidden = '';
 		$is_separator = false;
+		$screen = get_current_screen();
 
 		if ( $first ) {
 			$class[] = 'wp-first-item';
@@ -88,7 +89,7 @@
 			$submenu_items = $submenu[$item[2]];
 		}
 
-		if ( ( $parent_file && $item[2] == $parent_file ) || ( empty($typenow) && $self == $item[2] ) ) {
+		if ( ( $parent_file && $item[2] == $parent_file ) || ( empty($typenow) && $self == $item[2] ) || ( 'edit-tags' == $screen->base && false !== strpos($item[2], 'post_type=' . $screen->post_type) ) ) {
 			$class[] = ! empty( $submenu_items ) ? 'wp-has-current-submenu wp-menu-open' : 'current';
 		} else {
 			$class[] = 'wp-not-current-submenu';