Index: wp-includes/category-template.php
===================================================================
--- wp-includes/category-template.php	(revision 18970)
+++ wp-includes/category-template.php	(working copy)
@@ -552,7 +552,7 @@
 
 	$return = apply_filters( 'wp_tag_cloud', $return, $args );
 
-	if ( 'array' == $args['format'] || empty($args['echo']) )
+	if ( 'array' == $args['format'] || 'false' == $args['echo'] )
 		return $return;
 
 	echo $return;