I have this problem on a machine where gnome-btdownload is installed: at each world emerge, the version of bittorrent is bouncing between 3.4.2-r2 and 4.4.0. The problem seems to come from gnome-btdownload, requesting a bittorrent 3.4* version.
Nothing we could do here, p.mask >=net-p2p/bittorrent-4* if you want to use this. *** This bug has been marked as a duplicate of 48195 ***