Index: wp-includes/widgets.php
===================================================================
--- wp-includes/widgets.php	(revision 11300)
+++ wp-includes/widgets.php	(working copy)
@@ -554,8 +554,6 @@
 function wp_register_sidebar_widget($id, $name, $output_callback, $options = array()) {
 	global $wp_registered_widgets;
 
-	$id = strtolower($id);
-
 	if ( empty($output_callback) ) {
 		unset($wp_registered_widgets[$id]);
 		return;