I'm using calibre 1.25 (32-bit) on a Win7 64-bit PC.
- emptied my Recycle Bin (RB). Bin icon shows empty.
- imported a book into calibre then immediately deleted it again. Bin icon still shows empty.
- opened RB to see if anything in it. Deleted book dir is sitting there. Closed RB without doing anything. Bin icon now stuffed with paper.
Actually, I rechecked. Bin icon fills with paper as soon as RB is opened.
Your guess is as good as mine