Basically, whenever I join a battle ground, my map jumps from my bottom right corner, to middle left. I can't unlock it and drag it or anything easy like that.
I've tried it with no other addons running, and no effect, still hops to the same place.
The map stores a separate window size and location for each battleground and view position and zoom settings. You would move the window or size it by dragging the title bar or edges of the window as desired and it will stay like that for that battleground.