2006 Roadster

When I bought the car (1 month ago) the dome light was not seated properly. So I showed it to them and they put it on the list of things to fix after I bought the car. Well they forgot and the damn thing just fell out one day while driving. I then realized it was broken, so I went to the dealership and showed them. They ordered me a new one at no cost and when it arrived they snapped it into place. Well now the new one just randomly falls out?? I confirmed it was indeed a new one and not the same broken one from before. Is this a common problem, should I take it back again? I mean, I have a brand new dome light assembly, nothing is wrong with it, why wont it stay put?