Radio keeps playing

[fun in dirt]

So my '07 Classic daily driver radio (aftermarket system) is acting weird. About 4 times over the past few weeks, I get turn it off, open the door to get out & radio continues to play. I also noticed that the dome light does not come on when this is happening. After several times of cutting key on/off and opening & shutting door radio will eventually go off.
Initially I'm thinking maybe the door jam switch is stuck & it never knows door opened (because radio is supposed to keep playing for about ?15 minutes after key off, if you never open door). But I can't even see a door jam switch anywhere.
Anybody got an idea what may be causing this?

Even weirder is our dually ('06 Duramax) has started doing the same thing recently ...coincidence?