I noticed bug when information about listened tracks appeared on Last.fm twice. I thought, this is due to I usually listen music through external player (VLC), which uploads information on Last.fm too. Perhaps, Subsonic developers should add feature (checkbox in player settings) don't upload information to Last.fm when using external player.
P.S. Even after disabling Last.fm upload in VLC settings, information appears on Last.fm twice. It's bug indeed.