I had that problem lately on a new box where "set -sg escape-time 0"[0] was not set in tmux. It feels so different and annoying I kept mashing the buttons.
[0]: http://superuser.com/questions/252214/slight-delay-when-swit...
[0]: http://superuser.com/questions/252214/slight-delay-when-swit...
I often use vim and so far almost never accidentaly save ":wq" file.