Mine was acting same way with old 1995 melted switch and still acting the way you described from time to time with 1996 switch.I just won't leave the car until it shuts the light (few seconds in minimum position).If I see it stays longer I shut it off manually as I know it will stay on.I have no idea why is that and think it'* not worth the time spent to find out what'* wrong. There are so many things that go wrong with these cars.
Recently my security light stay on all the time when driving. Security works perfectly by the book,only light never goes off while engine is running.Disconnecting trunk sensor didn't help,so I just will drive as it is since driveability isn't affected.
On the last note these cars sure help auto mechanics to feed their families. LOL
I like it anyway.