All of the boxes were plastic, except for one. There was some blocking in the way so I put in a shallow metal box for a wall switch in one location. When I went to install the switch, I noticed something was missing:
The drywall installer was apparently offended by the screw tab sticking out from the box, so he broke them off. Well, he only succeeded in breaking one off. The other one he just bent over.
Now any normal person would have just roto-zipped around the box and the result would have been perfect. I even had already removed the front plaster clamps from the box to make this super easy.
Any person with half a brain would also realize that if you remove the screw tab, there's absolutely no way to mount a switch in the box anymore since there's no longer anything to screw into!