Is that really the POST URI? i.e. what you see in Firebug/DevTools?
If so, while legal (I think), it is not customary to pass variables both in the URL (as is normal in GET requests) and in the payload (as normal in POST/PUT). So if you DO really send variables in the URL, I would convert them to attributes of POST, either by setting them as (hidden?) inputs in a <form>, or, if this is an XHR request, then as params input, e.g. https://stackoverflow.com/a/12676773 or http://www.openjs.com/articles/ajax_xmlhttp_using_post.php
I would like to emphasize that I do not work for Cloudflare and that even if you do pass variables in the URI, I’m not claiming that this is the cause; It’s just a guess.