It seems like the keyboard just stops responding at random in Ubuntu 14.04 as well. I did not have this problem in Linux Mint 15. Switching from a free version of Java to the official version seemed to help at first, but the problem has returned. Pasting with Ctrl + V may have something to do with it, but I have never pasted a URL. (See https://answers.launchpad.net/ubuntu/+question/252222)