Forgive me the terribly late answer, Nicholas.
I've found this to be the duplicate of this bug:
http://sourceforge.net/tracker/index.php?func=detail&aid=3154132&group_id=200378&atid=973262
I'll be happy to provide further information.
Here's the gdb's output:
(gdb) bt full
#0 0x0043cd4d
2011/3/9 Nicholas Marriott :
> What exact libevent version are you using?
libevent-2.0.10-stable
> Does it still happen if you start tmux with EVENT_NOEPOLL=1?
Yes, symptoms are exactly the same.
> Can you show me the output of the following in gdb:
Here you are:
> f 0
(gdb) f 0
#0 0x00
