Description:
tmux 1.9a will crash when panes are manipulated a certain way. I just was bitten by this crash

This appears to have been caught by upstream already in commit 78e783e7. Patch attached

Additional info:

TIME PID UID GID SIG EXE
Tue 2014-04-29 20:30:32 EDT 19731 1000 100 11 /usr/bin/tmux
GNU gdb (GDB) 7.7
<snip>
Reading symbols from /usr/bin/tmux...done.
[New LWP 19731]

warning: Could not load shared library symbols for linux-vdso.so.1.
Do you need "set solib-search-path" or "set sysroot"?
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/libthread_db.so.1".
Core was generated by `tmux'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0 0x000000000043f29b in window_pane_active_lost ()

(gdb) bt
#0 0x000000000043f29b in window_pane_active_lost ()
#1 0x0000000000440639 in window_set_active_pane ()
#2 0x000000000040f743 in cmd_select_pane_exec ()
#3 0x000000000040db2c in cmdq_continue ()
#4 0x0000000000428bca in server_client_handle_key ()
#5 0x0000000000433549 in tty_keys_next ()
#6 0x00000000004343b0 in tty_read_callback ()
#7 0x00007f97dc4ef72a in ?? () from /usr/lib/libevent-2.0.so.5
#8 0x00007f97dc4e5104 in event_base_loop () from /usr/lib/libevent-2.0.so.5
#9 0x000000000042b5da in server_loop ()
#10 0x000000000042bca5 in server_start ()
#11 0x000000000040576a in client_connect ()
#12 0x0000000000405b5f in client_main ()
#13 0x0000000000403af0 in main ()