Index: src/wp-admin/includes/file.php
===================================================================
--- src/wp-admin/includes/file.php	(リビジョン 32298)
+++ src/wp-admin/includes/file.php	(作業コピー)
@@ -146,7 +146,7 @@
 		$dir = get_temp_dir();
 	}
 
-	if ( empty( $filename ) || '.' == $filename ) {
+	if ( empty( $filename ) || '.' == $filename || '/' === $filename ) {
 		$filename = time();
 	}