Inbox counter does not decrement to zero, if the message in the inbox is addressed to self.

Steps to replicate:

• Find a PM with multiple recipients. 
• Do a Reply to all – so your name is also in the To list
• When your inbox show you got an incoming message (from self), open the message and watch the Inbox showing Inbox(0).
• Navigate somewhere else – and watch the Inbox become Inbox (1) again.