Apparently the FAA has said
this before and now they've said it again. It appears that it is a question is enforcement. 135 operators point their fingers at their POI's. (See article via link)
A case could be made, regardless of interpretation, that the POI sets a precedent by not enforcing, but.... So put that beer back in 'fridge...you're on duty.
FAA: On Call = On Duty | BCA content from Aviation Week