Not odd at all. OR and RS perform trajectory analysis based on equations of motion. They are not intended to idiot-proof your rocket. Internal rocket parts and tethering are inconsequential to the analysis they perform.
It would also seem that at least in OpenRocket it assumes the rocket and nose cone stays together. For example, I tried to do a simulation where the nose cone separates from the body tube, each coming down separately on their own parachute. I couldn't find a way to do it (would be surprised if I might have missed something too)