embedded album art lost when transcoding FLAC->MP3

[crimsonadam]

when i use DSub to cache songs from my subsonic server, it removes the embedded album artwork. I suspect this happens during the transcoding process.
Is there a way to preserve the album art.

In subsonic's transcoding page in settings i am using this:
ffmpeg -i %s -map 0:0 -b:a %bk -b 320 -f mp3 -

Thanks for your help.