I find that if I don't maintain a certain temp in the house year round that my paper starts to pull away from the walls on the edges and seams. It seems tied into the temp of the rooms. Might be moisture that is getting into the plaster and that is causing the glue to release. It is almost enough to make me want to go back to painting or panelling my walls again. That is my next step upstairs where there are nothing but plaster walls to work with.