Hi Mark,
First of all, thanks you for your answer … I know this is only a side tool for you but so useful for many 
Here is more information about my differents tests, with the hope that will be help you when you have some spare time to dig in it.
First question is when it happend? With the help of Dockers, I have played with many milestone builds (openHAB 2.4 Milestone builds). Your binding works well until milestone 2.4.0-M7, 2.4.0-M8 and further doesn’t work anymore.
Second thing I noticed (on M8 and further) is that if my device is powered ON when I start Openhab, the binding works well but If my device is OFF at openhab start or if I power OFF and ON my device when openhab is started, the actions isn’t reconnized anymore.
Again, thanks you for this tool. At the moment, I kept a container with a light milestone 7 and only your binding, sync with my main openhab 2.4.0 release with mqtt.
Best regards,
Mac_Fly.