Index: functions-formatting.php
===================================================================
--- functions-formatting.php	(revision 8862)
+++ functions-formatting.php	(working copy)
@@ -291,6 +291,9 @@
 	// If strict, reduce to ASCII for max portability.
 	if ( $strict )
 		$username = preg_replace('|[^a-z0-9 _.\-@]|i', '', $username);
+		
+	// Consolidate contiguous whitespace 
+ 	$username = preg_replace('|\s+|', ' ', $username);
 
 	return apply_filters('sanitize_user', $username, $raw_username, $strict);
 }