I am having the same issue. It is bad enough in MM7 that I nearly gave up and requested a refund, but I'm sticking it out for now. It is the worst when traveling North or East. It must be somehow tied to strafing, since attempting to strafe in these directions produces strange movements. It is as if when I travel North, the game thinks I'm strafing north. There are times when I load the game where I can move freely as normal, but the problem appears within minutes. I have not pinpointed what starts the problem yet (initiating turn based combat, changing zones?)
The same problem seems to be in MM8, although to a lesser degree.
Another issue that may be related is that my arrows and projectile spells miss by a significant margin at medium to long distances. But not always.