Steps to reproduce:
At this point tmux server crashes, both sessions are lost and I'm left with two useless terminals (until I reset them).
Interestingly, step 4. (resizing the window) seems critical: if the two terminals are of the same size, session 0 exits while session bar remains, as expected.
This was observed with tmux version 1.6 (default packaged with Ubuntu 12.04) and with version 1.8 (downloaded from SF and compiled locally).
Bash version: 4.2.25(1)
Gnome-terminal version: 22.214.171.124
uname -a: Linux **** 3.2.0-54-generic #82-Ubuntu SMP Tue Sep 10 20:08:42 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux