Index: wp-includes/plugin.php
===================================================================
--- wp-includes/plugin.php	(revision 21059)
+++ wp-includes/plugin.php	(working copy)
@@ -282,8 +282,10 @@
 	global $wp_filter, $merged_filters;
 
 	if( isset($wp_filter[$tag]) ) {
-		if( false !== $priority && isset($wp_filter[$tag][$priority]) )
-			unset($wp_filter[$tag][$priority]);
+		if( false !== $priority ) {
+			if( isset($wp_filter[$tag][$priority]) )
+				unset($wp_filter[$tag][$priority]);
+		}
 		else
 			unset($wp_filter[$tag]);
 	}