What is truss uplift? Is this dangerous?

We live in a 3-year old house, a bungalow with an open floor plan. It’s divided down the middle by a wall and several sets of pillars. We’ve been in the house for three winters now, and every year the ceiling lifts at least 1 inch upwards from the walls around the kitchen and the support pillars. After our first winter we hired a home inspector to assess the problem, and he identified that our roof is framed with trusses. So far we’ve relied on the builder to repair the problem, and while he’s been responsive, I’m still not satisfied. He put quarter-round and crown molding around the top of the pillars and walls, and though the ceiling still rises and falls, we can’t see the movement. This doesn’t seem like a proper fix, though I also wonder if there really is any problem at all. Is this an issue? Can you think of anything that we or the builder can do to stop the movement once and for all?