That is not what is going on here... These parts are not under any extreme stress or anything. and btw pieces have NEVER just moved on me in ksp, ever! Even when they are under extreme stress as you say, and the stress is lifted, the part (if undamaged) will go back to its original position. This is a bug, cut and dried.
Let me be more clear. In the "VAB" when I simply test stuff with the DLC parts (IE a hangar door going up and down via piston or hinge) parts begin to drift away the more I work on it. Reverting a test from the launchpad will almost certainly result in the DLC parts drif