Index: wp-includes/widgets.php
===================================================================
--- wp-includes/widgets.php	(revision 38721)
+++ wp-includes/widgets.php	(working copy)
@@ -278,14 +278,16 @@
  * Removes a sidebar from the list.
  *
  * @since 2.2.0
+ * @since x.y.0 The `$name` parameter was changed to also accept a numeric sidebar ID. 
  *
  * @global array $wp_registered_sidebars Stores the new sidebar in this array by sidebar ID.
  *
- * @param string $name The ID of the sidebar when it was added.
+ * @param string|int $name The ID of the sidebar when it was registered. 
  */
 function unregister_sidebar( $name ) {
 	global $wp_registered_sidebars;
 
+	$name = ( is_numeric($name) ) ? "sidebar-$name" : sanitize_title($name); 
 	unset( $wp_registered_sidebars[ $name ] );
 }
 
@@ -296,13 +298,14 @@
  *
  * @global array $wp_registered_sidebars Registered sidebars.
  *
- * @param string|int $sidebar_id The ID of the sidebar when it was registered.
+ * @param string|int $name The ID of the sidebar when it was registered. 
  * @return bool True if the sidebar is registered, false otherwise.
  */
-function is_registered_sidebar( $sidebar_id ) {
+function is_registered_sidebar( $name ) {
 	global $wp_registered_sidebars;
 
-	return isset( $wp_registered_sidebars[ $sidebar_id ] );
+	$name = ( is_numeric($name) ) ? "sidebar-$name" : sanitize_title($name); 
+	return isset( $wp_registered_sidebars[ $name ] );
 }
 
 /**