The keyword here is "expected". Yes, you expect these to be timestamps, but they are $_REQUEST's which in WP is an array of $_POST and $_GET. They removed $_COOKIE from $_REQUEST in load.php. You should never expect anything when you're using $_POST, $_GET, $REQUEST, and most of the $_SERVER parameters. If someone wanted they could fire up anything from tamperdata to wireshark, to fiddle, their favorite tool and change what you expected to what they wanted.