There have been some strange issues with WAMP on some versions of PHP. I have had problems that would go away when I inserted debugging statements into the code to see what was happening.
What works for me is WAMP 2.2D (apache 2.2.22, PHP 5.4.3, and MySQL 5.5.24) Maybe you should give that a try. We have never installed XAMPP since WAMP was sufficient, so no idea on that combination.