I have two boards that share some card buttons. The "Grind" board for high-priority tasks, and the "Ideas" board for lower priority tasks. I want all the cards on either board to have a "Done" button, which will send them to the "Done" list on the Grind board. I want cards on the Ideas board to have a "Send to Grind" button that moves them to the Grind board. I also want cards on the Grind board to have a "Postpone" button that sends them to the Ideas board.
I set up the card buttons, and it all works as I want it to when I access trello.com on my computer.
So far so good.
Then I downloaded the Trello app for iPhone, and initially it looked like it worked. This shows a card on the Grind board and a card on the Ideas board when I initially looked at them:

But when I went back to that card on the Grind board one minute later, the button had changed:

If I delete the Trello app from my phone, and download it again, I get the correct card buttons. But the next time I check the card buttons, they are not right.
Is this just a bug? Or am I not understanding something about how this is supposed to work?