It's because of the way they attach the phones to the kiosks. They stick something on the battery door and inevitably when someone pulls on it, it pops the door off. They need to find a new way to attach the devices to the tables basically.
There was one post on here that a user reported his battery door was lose. Took it back to them and they tried one from a different phone and it fit snug. They ended up ordering him a new one. So I think there may be some random issues floating around possibly. Nothing in mass though or it would be all over this forum for sure.
I was looking at the display Nexus at the store Thursday while waiting for the lady to go get me one from the back. I picked the display model up off of the stand to take a closer look, and the stupid attachment thing ripped the door right off of it. Everyone heard it fall back down. I was just standing there like, "WTF?" Woman ran up and fixed it for me. I'm sure they put tape on that one at some point during the day.