I was on the loot screen and then I started messing around with the items in my inventory. I picked up the Cheap Spear that is isolated there in the screenshot. I dragged it to the right of my inventory (where it is in the screenshot) and with the left mouse button still held down I clicked the right mouse button to bring up the item's card suite. With the card suite enlarged I released the left mouse button and then closed the card suite window. Now the Cheap Spear is stuck there. As I drag the screen around it remains in the same position on my monitor (ie. everything but the spear moves as expected). Once I left the loot screen the spear was returned to my inventory and was no longer displayed on the screen. Edit: Actually added my screen shot <_<
Ooh, this might explain how I got a card suite stuck on the screen once: I was fiddling around with mouse buttons, and it's possible that I did the same sequence as you. Worth checking to see if mouse commands can get crossed like this reliably.
