I wasn't able to reproduce the bug on Ubuntu 13.04. However, I had to use 'sudo usermod -m -d /home/user2 -l user2 user1' instead of the GUI, since Ubuntu 13.04 no longer includes a GUI for changing the username.
I wasn't able to reproduce the bug on Ubuntu 13.04. However, I had to use 'sudo usermod -m -d /home/user2 -l user2 user1' instead of the GUI, since Ubuntu 13.04 no longer includes a GUI for changing the username.