This is also happening to me.
The search functionality is also lost when searching for pages as well as users.
Disable the NUA plugin and all works well!
Unfortunately i am also having this problem.
I installed it first – no problems.
Trying to identify an issue i uninstalled it.
Then after finding out my “rogue” plugin – reinstalled it!
Now when i send an email – the mailbox shows one email
but my posts start to fill up with the same email, 22, 23, 24 and so on!
Please help as i really need this to work!
