Prevent Logoff from Killing tmux Session

I have noticed that a logoff (log out) from my X user session will kill any tmux session I have initiated, even sessions I had run with sudo tmux and similar commands. I am sure that this formerly did not happen, but some recent change has effected this behavior.

Force title on GNU screen

By default, the title of a screen session is the name of the last command entered, which is fine for me, but in some cases I’d like to change it. I know the command CtrlA A, but it only changes the title until the next command, and I’d like it to stay there until I decide otherwise.