You are right. I've been able to reproduce the bug by shutting down the upower service and restarting powerdevil so it wakes up upower and it's easier to trigger the same race condition.
This doesn't fix it, so I've changed the commit to CCBUG.
I guess we need something like !377 (closed) in addition to this, but even then it's a race condition of when DBus paths (not services) are created, which I haven't found a way to get notified of.