We have exactly the same problem. We painted over the old paint and it just wrapped arround the roller in sheets like you stated.
We are now in the process of *trying* to remove all the old paint but cant get it all off.
Tryed a heat-gun and that popped holes in the plaster, tryed steaming out the room, but that didn't help...
Does it all need to be removed, and if so-- how ?!
Should you use 'paint for new plaster' over the plaster in a bathroom before the new paint is applied?