chunter, it is strange to me that you find a Leupold has this problem.
I have one 6,5-20x50LR VXIII in my .308 and have tried several others of my friends, and find they're all dependable or reliable adjustments, both for the vertical and horizontal. (i can easily change them in some ranges, from 100 to 300m, back to 100, then to 200, 400 etc. and the p.o.i. is always right).
So far i find that Leupold is a very good one on this. In other side i can not depend on cheap scopes in this thing.
If you have the problem, i suggest you do as Jose have advised you.