Gmail messages switching to unread after I view them
iPhone 5s with iOS 7.1. I use Gmail in the default mail app, meaning it's an IMAP connection.
When a new message arrives, I open it on the phone. As soon as I do this, it changes the status to "read" but within a second or two it goes back to "unread". I have to manually mark it as read, or close the message and open it again to have it appear as read. It happens regardless of whether or not I read the message the instant it arrives, or if I read it sometime later.
This has been happening since before 7.1. I don't remember precisely when it started. Tried deleting the account and re-adding it. I don't have mail clients open anywhere else that might be changing the status unintentionally. It doesn't happen to my Exchange account in the mail app, nor does it make any difference if I'm on a wifi or cellular network. The push interval is 15 minutes, if it matters.
I'm getting quite frustrated with this. What am I doing wrong here?
iPhone 5s, iOS 7.1