I think I didn't understand your original problem ... I just did the following :

1) Made a random playlist "test"
2) Copy Artists + Mirror Paste into "test"
3) Copy Genres + Mirror Paste into "test"
4) Copy Years + Mirror Paste into "test"
5) Sync
6) Delete Artists Mirror
7) Sync

What I THOUGHT you were saying was that Artists wasn't going away when you synced, but it goes away for me, so you must be saying something different ... Can you give me a little more info on what you're seeing/asking for?

Thanks
Mike