I'm still curious - why do you have the Blizzard minimap "docking"? That could actually be causing your problem.
I remember having the same trouble with the minimized map about three years ago (it could be longer ago, but my memory isn't all that sharp anymore
). I cured it, I think, by making the minimap go full size inside. It is (or was) part of the options for the minimized map. Once I did that, I didn't have that particular problem again.