yeah,i delete all my music on phone, then use itune to convert my music to m4a, delete the mp3 version of them on itune, then sync with wp desktop app.
somehow, it put a folder cover to each album on your phone... and it work ...
Sorry for my bad English
I have found a solutions for this problem, follow these step and it may work:
First, Add your music to iTunes
> EDIT Tag with ""get Info" in iTunes
> then Create a AAC version of them
> sync your music to your phone with window phone desktop app...
It work for me...