There are at least two distinct ways to move an item via dimension edit in the Family Editor, but they can have very different results. See video:
My video is directly derivative of one from Steve Stafford last week. Steve demonstrated some interesting behaviour along basically the same lines at:
Revit OpEd: Two Minutes with Constraint Quirkiness
Had this same issue. Check out the anchor icon on the eq dimension. Highlight the outer RP's and drag the anchor to the centre RP for expected results.