Index: wp-admin/includes/media.php
===================================================================
--- wp-admin/includes/media.php	(revision 22852)
+++ wp-admin/includes/media.php	(working copy)
@@ -734,6 +734,7 @@
 		if ( empty($check) )
 			$check = get_user_setting('imgsize', 'medium');
 
+		$out = array();
 		foreach ( $size_names as $size => $label ) {
 			$downsize = image_downsize($post->ID, $size);
 			$checked = '';