Possibly related bugs with different reported symptoms:
Bug 1014507: Drag & Drop of window to other desktop separates mouse position from window position Bug 903846: cursor is placed much above the window border after dragging a snapped window
Possibly related bugs with different reported symptoms:
Bug 1014507: Drag & Drop of window to other desktop separates mouse position from window position
Bug 903846: cursor is placed much above the window border after dragging a snapped window