If I remove the on/off module from the receptacle then there is no interference with the ceiling light).
If I attach the on/off module to the receptacle and manually keep the unit in the OFF state then whenever the motion sensor gets triggered I do get the ceiling light interference (no programs running).
I do not have other Insteon devices at this time, so cannot check their interference.
I therefore conclude that the on/off module is communicating with the eisy - but why if I do not command it to do so?
Does the on/off module behave as a repeater of the sensor rf?