Are you working on a laptop with a touch panel? Sometimes the mouse control gets messed up when you accidentally touch the panel with the thumb.

Apart from that, I haven't heard of any particular mouse problems in WED yet. Check out whether this affects more programs on your PC, or only WED - f.i. if you can move or rotate objects in MED. Also, try it with another mouse, just in case there's something wrong with the mouse hardware.