I play GTA IV on my PS3 and sometimes the engine reacts a bit weird, and that is where the bugs come in. Sometimes your car gets all crumbled up with just a tiny, single hit and sometimes you can hit objects with full speed but not get any damage. Same with the effect that you fly through your windshield. Sometimes you fly through with just a tiny hit, sometimes you don't fly out when you hit an object / vehicle at full speed. Etc.