Downstream report is here:

https://bugzilla.redhat.com/show_bug.cgi?id=545267

Relevant quote:

okay after about 20 reboots I got this to happen on my system with the latest
dbus and consolekit.

It looks like we're hitting *another* bug by being the first user to use
ConsoleKit.

There's one thing that looks suspicious in the ConsoleKit code.  We take a name
on the bus before we register a handler for the call GDM is making.

So the race could be something like:

1) GDM calls OpenSessionWithParameters
2) d-bus notices consolekit isn't running and starts it
3) consolekit starts up and takes a name on the bus
4) consolekit registers handlers for the methods it supports
5) consolekit enters its event loop to process events


When the d-bus daemon notices ConsoleKit has taken a name (step 3) it delivers
the pending gdm call.  If that happens before step 4 then it could explain this
behavior.