So, i havent found a proper way of doing this either, however if you are desperate, here is a painfully convoluted way of accomplishing what you desire:
First, load up the tracks you wanna drag over, if its just an album then load that up and hit play.
Then, Go the your ipod on the top right,
Finally, click the "up next" button (next to your currently playing song **you should play the song right before the ones you want to transfer) and drag the songs you want from there.. (this can be done from a playlist, etc...)
Not sure what the F apple was thinking making manual music managment impossible or at least not obvious.
This whole update p*sses me off to no end, probably gonna downgrade until they fix these issues.
Anyone REALLY like the fact they moved everything around? H3LL NO. i like the new features, just dont make it harder to do everything! LESS IS NOT MORE. Soon we will just be pressing one button to play, pause, skip, sync, jackoff, etc... depending on our moods?
I would like a proper answer to your question. From Apple. Maybe a reason for all this nonsense while their at it.
EDIT:
This issue seems to only arise when you are pulling your tracks from a playlist.
This is indeed an issue and needs to be fixed. Especially if you are like me and do all your playlist editing on itunes and then want to simply drag a playlist over to your ipod/phone