scrobbling a streamed mp3 does not work

Greetings,
I have been using winamp as my fav. music engine. Recently i have installed a network device which allows me to stream mp3s, i.e. i add mp3s using Play Url (Ctrl-L).

While Winamp reads the id3 information of mp3s, last.fm plugin fails to scrobble my mp3s.

Is there a setting somewhere i am missing? Or is this simply not (yet) possible?

Cheers

EDIT: scrobbling works perfectly if I play media files residing in local folders.