Post-command hooks are sometimes being called twice

[wilbaker]

We've had reports of the post-command hook being called twice.

The current theory is:

[...] something called die/exit while we were running
child[3]. There's a race in run_post_command_hook() that would allow child[4]
to still be started.

[jeffhostetler]

Could also be that the post-command hook could not be launched (for example, access denied or missing dll or something). This would cause the exec/CreateProcess to return -1 and that could
(I haven't checked the code yet) start shutting things down and cause the atexit() code to run.
Just a theory at this point.