Yeah that does work. But I don't think the gangbank was meant to hold this much anyway. Especially since it's not limited at all using the bank all feature. Which could lead to negative banks.
Thanks for reporting this. We'll look into getting it fixed for the next version. The limit indeed was supposed to be 200,000,000 but since most people have already banked more than that I don't think it will be a good idea to cap it now.