so I've played around some more. very mixed bag. soundwise. I do get the feeling that many, if not most, of the waltz tracks have very limited audio material to work with and therefor create a lot of very unnatural sounding tracks with a lot of repetition. At least that would explain quite a lot of what I'm getting.

one thing that really sticks out though: every single "solist" or "background" waltz track will only generate the very first bar when the time signature is set to 3/4.

they all render correctly when it's set to 4/4, but then again, that can't be how this is meant to work, can it?