I'm not going to say that it's not your cookies, but I doubt that it is.
this (so far as I can see) is why it's happening.
You are donating to someone, once you have finished donating, your get the thank you message, which is being generated by from the itemshop.php file, you are then going to the itemshop.php file, which your browser is not updating because it thinks it's the same page you want displayed, but it's not.
I hope that makes sence? it does to me