Unread mail inbox problem "No Message Selected"

This issue has affected my iPhone 6 ever since I upgraded from iOS 8.1 to 8.2. I have restored and wiped my phone numerous times. I upgraded to iOS 8.3, and now 8.4 and the problem is still there. I even tried removing my email accounts from the mail app and re-adding them.

As you may know, there is a smart inbox feature in the mail app that allows you to see an Unread Mailbox featuring the unread mail of all connected mail accounts. This is great and the feature works fine for the most part. Here is the issue that I am thinking is a bug:

If you have the Unread Mailbox open, when you close the Mail app and re-open it, the Mail app usually opens in whatever mailbox you had open last. However, when I close the Mail app and re-open it, my Unread Mailbox will be blank and say "No Message Selected." At the top left is < Unread. If I tap < Unread, then my unread mail will re-appear. This bug only occurs if I have unread mail in the unread inbox.

Any ideas on how to fix it? To recap, when I open the Mail app to my Unread Mailbox, my Unread Mailbox is blank and says "No Message Selected" unless I tap < Unread to go back, then I end up seeing the unread mail.