Unable to part exchange a 120 NFL Boss for another 120 NFL Boss

I'm Unable to part exchange a 120 NFL Boss for another 120 NFL Boss (trade Boss for x7 emblem pack using 120 player trade-in screen in NFL Bosses menu), The player simply doesn't show on the 120 player trade-in screen when benched from roster. Has anyone else come across this issue. I assume it's a bug as there was no information given at the time of obtaining the player stating that the 120 NFL Boss players couldn't be traded back. If it's not a bug I would like to know the point in stopping us from trading the 120 NFL Boss players back. Thank You in advance for any advice/suggestions!