A couple of times in the last week I've dragged a file from a Finder window into the attachments pane and lost the file. Visually, the file appears to snap back or bound back to the Finder window but it's not there. Nor is it in PB. Nor trash.
It may be happening when dragging over a file to replace it. It's not every time though and other files drag-drop no problems.
Lastest version of PB on Mac OS X Lion.