Radio stays on when engine is turned off?

I have a strange problem with my 2014 Fiesta SE. Occasionally when I turn the ignition off, the radio continues to play and nothing can be adjusted on it. You can't turn it off by hitting the on/off button, can't change station or adjust volume. My local Ford dealer suggested disconnecting the positive battery cable for a few seconds and then re-installing it to get the radio to re-set. This works. However, the problem continues and I do not know the cause or the solution. Any ideas?
Unfortunately I have not. The first couple of times this happened, it was in the winter when the outside temperature was really low. Then, it happened this summer, so temperature apparently is not a factor. If you discover anything, please share. Thanks for responding to my thread!


It'll continue playing for about 30 minutes and should shut off by itself.
My radio has played for over an hour when I have disconnected the battery. I have never tried to see how long it will play on its own. Guess I am afraid that it will eventually drain the battery.