Upstart Loses Track of Services ("Unknown instance")

[Richard Laager]

I have this recurring problem where trying to stop services results in
"Unknown instance". It's as if upstart has lost track of the fact that a
service is running (and its PID); starting the service again will result
in two copies running (at least for some services that don't do their
own duplicate checking).

It has continued to happen across several releases of Ubuntu, with
multiple different services (e.g. SSH, upstart jobs for daemons I've
written myself). With SSH, it's virtually guaranteed to happen every
time I want to stop it (since I do so infrequently), but I can't
reproduce this on demand. In other words, I can
start...stop...start...stop services right in a row to my heart's
content and it's fine. I'm starting to wonder if the trigger isn't
something that happens nightly. Alternatively, it might be happening on
(certain) package upgrades.

What should I be doing to debug this?

-- 
Richard
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