I am getting exactly the same problem. I did a google search just now specifically to see if anyone had opened a post about this bug. Yes it coincided with WP 4.4. The problem is by far the worst with Chrome but same thing will happen with other browsers too. The more text I am pasting (in my case tables) the more likely the problem. In chrome it is unworkable, though. The moment you paste it goes to “Aw Snap”, not even when you save. It happens when you paste.