I always keep my recycle bin empty, but if I didn't then I would be curious to know if the recycle bin is used in the disk quota or not. I'm going to have to experiment tomorrow unless someone knows the answer to that already. I also wouldn't rule out hidden files or system files interfering. I don't have any experience with Teracopy.
Personally I would slap that USB key on a Linux machine to see what is there for hidden files, but it can be done on a windows machine as well.