This is because of certain classes (like a Demon hunter, for example) that can't wear certain items in their offhands simultaneously, so it moves your gear-over. I'm not sure how to work-around this, but I know at least barbarians and monks can use the mode fine for now. It'll probably require more tweaks for other classes, and any tweaks (for example moving your gear back to their original spots) will slow-down the script (mouse dragging items) which may not be entirely enjoyable or "snappy" as it currently is.