Very unusual, do you know what purpose the "balloon" serves?
I don't know. There isn't that much information out there and I don't know if any animal interactions/pollination have been observed (How long did it take for Angraecum sesquipedale pollination to be observed?).
Feel free to track down the taxa-paper (and any other relevant info) and post the link here.
Amazing! I acquired my own little specimen of Bulbophyllum physometrum earlier this year, and I've got my fingers crossed that It'll flower some time this year. Really beautiful, weird flowers. I love them