http://www.youtube.com/watch?v=nt79OFcrgqU

(I'm not sure why Fraps recorded the cursor offset like that...it looked fine in game)

What you're looking at is me dragging items in my bag from slot to slot. But one slot in particular seems to be a "black hole". Items dragged there disappear and never return.

I logged out and back in a couple of times and continued to have this issue. However, the spot where items would disappear into would change. In addition sometimes I would move something but when I let go of the mouse button a different item would move instead.

edit: I just checked and this happens on all my characters. My character names are Walter Hyde (the one I first noticed the issue on), Walter Taylor, and Walter Gunn.