I just checked and what happens since I think 0.9w-8(maybe -a) is that it now needs a click on the track first to highlight it. Before this was done automatically.
As far as I can see this only doesn't work (anymore) at dragging files onto the Playlist Area. All the other means are still OK.
Anyway, dragging needs one additional click.
Will be solved in the next version. But if you want I can upload an XXHighEnd.zip right here. You just need to say it ...
(but I try to avoid confusion with such loose hanging around versions ... in the end it will be me making mistakes around that
)