I just noticed something that could be related to this. I think it's always been there, even in AH2, though.
The mouse-over pop-up sometimes appears "randomly" on the screen. Moveing the pointer clears it. The pop-up is triggered by opening/closing the clipboard. However, it doesn't open "under" the mouse pointer (at its position), but the opening/closing motion just passes through the pointer.
As a result, there's the popup saying "click to drag..." with nothing under the mouse pointer that could be dragged. Sometimes, it even pops up when closing the clipboard.
