Hover over a visitor tab item such as your account menu, and click into the editor. It doesn't close. Click anywhere else on the page, and it does close.
This behaviour isn't new. It's the same on TinyMCE too. So it may just generally be an issue with contenteditable areas, but it might be more of a prevalent issue now when you consider more AJAX events happen now that may trigger new alerts or conversations to be looked at quickly while in the middle of typing a message.
If it's fixable, great. If not, meh.