A non-hypothetical but abstracted situation:
I have a domain www.foo.com, from which I'm making an AJAX POST to beta.foo.com. Examining the XHR object, I see a response header of 200 OK, but no response text - I even get a response 12B long, which is the exact response (a 12-character string) that I'm expecting - but the response text is blank.
If this is a cross-domain issue, why am I getting 200 OK, and better yet - why am I seeing the PHP functions fire on the beta.foo.com side - yet getting no response?