A diode fixes the problem for those that are experiencing it. It's very rare, happening only in cars that generate a huge negative spike on their switched power line when the ignition is turned off. By huge, I mean around -50V for several milliseconds.

We've ordered some male->female ISO cables which we're going to build the diode into so it will be a simple plug-in fix. I'll mailshot owners soon to establish who's affected.

Rob