That's not possible(size without compression wouldn't fit at all - it'd be the size of your rootfs tar file). The only thing I can think of is perhaps there's some temp files(tracker lists, thumbnailer) that got copied back but the program in question ignored them(essentially creating duplicate images/lists).
I will see about adding /var/tmp/tracker-user/cache.db into the next backup, see if that changes anything.

edit:
I'd also try creative use of "du -h" to figure out where your space is going.