Hey, my name is Paul you insensitive clod!

(Note: That is a common internet meme and there is no malice behind it. It's supposed to be funny standing on it's own. Of course if the mods disagree then delete with my apologies).
But to get back on topic: Have you tried resetting the phone (holding in both buttons until it reboots). I assume you are on 6.1.3 because of a JB? (May be a dumb thing to say because I don't JB and otherwise not sure why you wouldn't be on 6.1.4. Just my ignorance.
Because I don't have a quick answer and didn't see anything on a quick Google, I'd recommend removing all your mail accounts and add them back one by one to see if there is a particular one that causes the issue. Heck, grab a free account from somewhere and give it a try. To be honest I haven't heard of this one before and I can't speak to Gmail because I don't use it. Good luck!