I never called them about an issue, because I didn't buy the parts from them. I bought that lower already built, from a member here, but that was specifically listed in his parts list - hell, we helped him build that rifle. That receiver extension is too deep, and that fuckin' spring is weird. It doesn't even go (belong) in an AR15.
Brother, I'd say just buy some quality mil-spec AR15 carbine receiver extension, and the Armalite EA1095 spring, and run it. the buffer they have is good - measures out, and it's a heavy little fucker.
For them to say no one has had an issue - well, maybe nobody has told them that there's an issue. I sure as hell had an issue with it, though. <dontknow>