Have you tried it with any other styles? I randomly grabbed a few different styles and had the same result with all of them. I could change the style as a whole, and I could change any other track, but the drum track would not change for any of them.

Side note: I also could not turn off the multidrum feature either. I'd go in, hit "default" - which would clear out all the setting - then hit "ok," but it would not turn off. And when you reopen it, the original settings were still there and on. Its like it's not saving any changes being made to the drums.