Nah, that's not the sponsor thing I think, at least not a single case, I could be wrong though. I tested on a few. I think it's just the way php and web browsers work, same with javascript, it would not pass the referrer. But server redirection on the other hand like in htaccess would. I believe though there must be some way to trick browsers with php to pass it. Reading stackexchange at the moment, but the more I read the more mess is in my head and it's already suffering tonight from a headache.
So I have thought, that perhaps someone here done it before and will save me a bit of time and struggle.