Garage Door reporting open when closed

Strange thing started happening recently in the Home app. My garage door is being shown as open when its actually closed. This started perhaps a week or two ago. Since then I've stoped/re-started the HKB device that its part of, stopped/re-started HKB itself, stopped/re-started Indigo/rebooted the machine it runs on. Can't think of anything else to try. The garage door shows properly in Indigo itself, its just in the Home app that it is incorrect.

Oh, and yes, I've tried deleting it from the HKB device and re-adding it, both with and without the "invert state" checked. Still no joy.

Even stranger, we had a prolonged power outage last night (~3 hours) and when everything came back on it was reporting correctly. Then about 30 minutes later it started reporting it was open.

Fortunately I've got a camera in the garage and can easily verify that the door is really closed.