Using KTorrent 2.0 Beta1 (Suse package from Guru, has some patches) I observed a tracker doesn't admits when I complete a torrent. Probably the problem is that KT20B1 is sending meessages with event=completed and left!=0.
I only monitorized a packet, but it included a "left=524288", and yes, pieces were of 512KB.

I think, the stats are not updated yet when we do the completed announce.

I have fixed it.