You can switch what's in your bank by changing the storyteller BEFORE pulling from bank. This may be what's happening to some here.
ETA: it's risky and sometimes doesn't quite work by a couple. But say your town has 20 spawned from campfire you just released. 40 go into bank. If you need less than 20 to upgrade to next level, you can set the storyteller right away to the next currency. The 20 in your town will level you up, and the 40 from the bank will turn into the next currency. You may have to synch with friend screen at an optimal time to switch the next 40.