Bolero - USB mobile charging - prevent muting of DAB radio

Apologies if this was covered already, I tried a search and didn't come up with what I was looking for.

Basically, my Bolero stereo, if I plug my Android phone in to charge, it thinks I want to play music off the phone.

If I select Radio again to go back to DAB, this is muted, even if I turn the volume up.

So my question is, is there a way of stopping the Bolero from doing this? Allow it to charge *and* listen to the radio?

Thanks!