To reproduce:
1) Open the attached project that user sent(later one) and load scene 'BugTest'
2) Run it and switch to scene view
3) Check the place of B game object, notice that it located left from form A object, this is expected.
4) Now check game object C collider, it have not moved with it's parent to left side. It should have moved along with it's parent.
5) Try to move B object a bit with x or y position arrows, notice that it snaps into it's place immediately.

This is a duplicate of: http://issuetracker.unity3d.com/issues/rotating-a-parent-gameobject-rotates-the-childs-sprite-but-not-collider