Thanks for providing this information. I did not know that. So basically the Bittorrent applications offer no security, encrypting the shared files with your information regarding the real IP right?
The above mentioned torrent clients have this bad behavior, in some circumstances (they put an IP address inside some packets they send out, under some circumstances). Please note that this bad behavior is irrelevant if your system is connected to an OpenVPN server, because in the worst case the torrent client will be able to transmit the VPN IP address only, not your real IP address.
The behavior becomes potentially dangerous for your privacy if your torrent client connects to a proxy, or if you use a PPTP based VPN.