Although I'm pretty late to the party here, I have been seeing the volume bug since 12A Mk1. Symptoms are - leave home & get into car. Power on. Stop engine briefly to wipe blood from ears and go inside to change underpants. Return, try again, only this time stomping on the volume immediately to pull it down from 0dB (house settings). Get to work, plug in, sit there for 20 minutes wondering why it's so quiet. Realise there's something up, check volume to find it's still at the setting I left it at in the car. Wind it up to 0dB. Make pathetic attempt to justify my salary. Finish pathetic attempt. Go out to car to go home. Power on. Stop engine again to re-focus eyes, wipe away tears of joy/pain, go back in to change into remaining pair of undies. Come out and try again, stomping on volume immediately etc. etc. etc.etc.

I'm not very good at this bug reporting thing really

One of the few remaining Mk1 owners... #00015