Quick+Dirty fix for the drag/drop hover effect flashing on and off.
When a file drag is in effect, the upload dialog gets some special UI effects. The effects get turned off if there is no new drag event within 100ms. Irritatingly enough, sometimes the drag event would stutter for slightly longer than 100ms, causing a freaky flashing effect when you stopped moving the mouse during a drag. I bumped that timeout to 300ms to hopefully avoid that.