The solution it seems is to report the problem on this message thread - crossed fingers, but no more occurrences since. Next there is that annoying, intermittent warning bleep with absolutely no indication of the reason...

I had the same issue. If it gets really annoying (it does) a work-around seems to be to go to Navigation > Menu > Settings and set 'Last Charging Station' to OFF. Since doing that, the warning has failed to appear, but that may have been a coincidence. The latest update does not seem to be good (see my other issue raised about random reboots).