No sound from Clip + when plugged into car charger and AUX outlet

I got the Clip + recently, and it works fine when plugged into my car stereo’s AUX outlet.  Today I got the car charger for it, and when it’s plugged into the charger, it kills the sound. The battery shows charging, and the track is playing, but there’s no sound coming from the speakers.  Any ideas?

FWIW, I also got an AC charger, and it plays fine when plugged into that. 

Thanks!