I often create repeating patterns which (among other things) require dragging a selection of motif from the top to the bottom of square in order to create the repeat.
I'll select the portion to be copied and moved (just below a guide line), create a new layer (cmd+J), and drag this below my other guide at the bottom. But when I do this, the edge of the motif has a shadow, as though the selection didn't fully "grab" the motif. Feathering and anti-aliasing is turned off.
This seems like a huge bug (unless I'm doing something wrong, but then that wouldn't be intuitive).