Sounds like he's using wired phones though. This is a function of the hardware - if the phone jack is making contact one way, phones are active (wired, not wireless), the other, the speaker is active. Checking the wireless enable selection is a good start though. I can think of one scenario where that might possibly give this symptom, but I'm very skeptical on that. Sounds more like a phone jack issue to me. Give customer service a call.
If you are only using wired headphones, go to an audio menu (zoom an audio live control, or the audio menu in the expert menu or 6 block menu). Select "Wireless Headphone" press enter. Make sure that "Enable" is not checked. If that is not checked, then it's most likely the phone jack.