If my watch discovers that I am wearing a HRM belt when not in an activity, the watch will disable the OHR. Good!
However, it will not use the signal from the HRM belt. So the HR graph in the watch is empty for the time I have been wearing the belt.
Seems like a bug to me. Either the watch should keep the OHR turned on an use the HR from the OHR, or it should switch off the OHR and use the HR from the HRM belt. Switching off the OHR and then continue trying to get HR from the OHR will not really work.
I haven't had a watch with an OHR for that long, so I don't know if it is a new behaviour.