If you open the keyboard, then look at the back of the device, behind the device there is a plastic coating. My wifes phones coating is fine. Mine has little air pockets. I can massage them out, but they return. If I ignore them they get bigger.
I assume the plastic lining helps the slide mechanism.
Also my battery cover sometimes falls off, but its not too bad yet. Can we buy replacement battery covers, perhaps 3rd party?