Thanks for the telnet debug info. Based on the log I think the fourth device is responding to the Scene Group commands as if it were part of the Scene. What this tells me is that at some point it was a part of Scene_1 and then you may have deleted that scene and created another. But when you deleted the old scene, for some reason the link in that fourth device did not get deleted. I need to duplicate that and check what could have happened.
In the meanwhile if that fourth device is not part of any other scene, then you can factory reset that device and re-add it, this will solve your problem(temporary fix). I will check and let you know. Thanks for your patience.