Judging by posts in other forums, players of Austria in the Grand Campaign seem to be able to do this. Counting restarts from saves I have attempted this at least one hundred times! From one save-game point I ran an experiment vassalizing Baden and Hungary. Baden vassalized 5 times out of ten, Hungary zero. I don't know if this is a bug or not, but if its not the result of some strange odds calculation, how do I fix this annoying, and potentially VP damaging, flaw. I did try reinstalling; this fixed an annoying error message that kept cropping up when selecting the Netherlands shield, but not this.