Mail's "All inboxes" doesn't list messages from all accounts

I finally realized that I was missing seeing email messsages because I assumed that when Mail was set to “All inboxes”, it was still just showing messages from one of my accounts. That’s not the case on the iPhone. I couldn’t find a way to work around this. I look at the Apple Communities site and others have noticed this, too. Any suggestions?

Are you filtering to show only unread messages?

No, I’m showing both read and unread messages.

I find on my iPad Mail actually skips over messages when going through “All inboxes”, and I have to go back and manually select them from the main list to read them. No consistent reason why or when this happens.