I've set up two mail accounts on my iPhone. Whenever I go to "mailboxes", you can either enter one of your accounts or go directly to the inbox of one of your accounts. Whenever I go to "all inboxes", the back button shows the text "mailboxes", whenever I go directly into the inbox of account A, it shows "A" in the back button. This strikes me as odd, since both buttons refer to the same location within the mail app, so the text should be the same. I didn't notice it until today, but it seems like a bug that has been existent in iOS since forever. I think that's weird. Just wanted to share that with you.