WMP11 Sync Problem with Sansa c240

I'm encountering a problem in sync'ing music from WMP11 to my portable music
device. Here is what happens:

I have a saved playlist of songs that I drag into the sync pane. I then
drag over a whole lot of individual songs into the same sync pane. So, when
I'm finished, the sync pane shows the playlist at the top and then all the
other songs I want to sync. When I click "Start Sync", it sync's the
playlist songs just fine. It then stops and will not sync any of the
individual songs I dragged into the sync pane. I just sits there. The lower
right portion of WMP shows the "sync" animation but the progress doesn't move
and none of the individual songs will sync. I end up having to click "stop
sync".

Does anyone else have this issue? Is there a workaround? Is this is a bug?

Thanks,