DFPlayer standalone loops selected mp3

I have a DFPlayer that I want to use standalone - not controlled by an Arduino or whatever. I provide +5 vdc, connect a speaker, create the mp3 file as instructed - in folder mp3 named 0001.mp3 - on a micro SD card. When I trigger ADKEY_1 by briefly connecting it to GND, the file plays as expected but instead of stopping at the end of the file, it loops forever. I do not expect this to happen. What have I done wrong?

Dale Gloer