diff -ruN wordpress.orig/wp-admin/includes/file.php wordpress/wp-admin/includes/file.php
--- wordpress.orig/wp-admin/includes/file.php	2013-06-21 08:12:17.000000000 +0200
+++ wordpress/wp-admin/includes/file.php	2013-07-06 15:37:22.659830799 +0200
@@ -864,8 +864,7 @@
 		$temp_file_name = $context . 'temp-write-test-' . time();
 		$temp_handle = @fopen($temp_file_name, 'w');
 		if ( $temp_handle ) {
-			if ( getmyuid() == @fileowner($temp_file_name) )
-				$method = 'direct';
+			$method = 'direct';
 			@fclose($temp_handle);
 			@unlink($temp_file_name);
 		}