Sorry, but I think there is a mess here.
"Example: Yoda has buff block, no other ally does. Use Battle Meditation and no ally gains buff immunity"
Yoda's Battle Meditation grants every other ally just POSITIVE status effect - buff immunity is not positive.
Yoda's Battle Meditation is a little bit different because he should first gain Tenacity up and then give it to allies ,obviously buff immunity blocks it, so there is nothing to give.
I am not sure, but I think that if you use different mass buff ability it should be granted to allies which does not have buff immunity - for example AA Tactical Genius should grant buff to allies which does not have buff immunity
EDIT: anyway this is not a bug