I've been very happy with my Interarms built Polish Tantal (pretty much an AK-74). Mine certainly gets hot if you put rounds through quickly (I once gave myself a pretty nasty burn after accidentally touching the gas tube post several mag dumps), but I've yet to find a semi-auto centerfire rifle that doesn't heat up after fairly heavy fire. Heck even my bolt action rifles get pretty warm after only a few shots (my Mosin-Nagant has the lacquer smoking and occasionally bubbling).
Now that said, there could be a specific problem with the Bulgarian rifles but I've had good luck with my Interarms AK...so it's possible rumors would exaggerated.