Does your feature manager tree have a "(-)" in the tilted part?
If yes, there's not enough constraints in your part and it can move or tilt in any moment (if you insert another component and start to making mates, the unconstrained part will move)
If no, then your part is constrained, but you have not done properly the mates. You must revise your mates to find out what is causing this behaviour and modify it (or delete it and make a new one).
Regards