I bought an Expedition a couple months ago, never realized the back windows did that and never noticed that button in the overhead lights...
My wife turned on a map light one evening, turned it off.. no problems.
Next day Im driving my kids to daycare and in the side mirror I notice the back glass is slapping open and closed a little on bumps.

I hope out, and realize I can move the glass with my finger! I call around for some prices to re 'set' the glass and seal it, the places I called did not answer..
i look inside and see the mechanics of the glass and figure it out...

boy was I relieved!