Hi Nigel,
This happened to me several times with both DP1M and DP2M, I think it may have happened because they were both without a battery for a longer period.
How that would cause only the date/time setting and not all the other settings to default is of course mysterious...
Then again, they are mysterious li'l black bricks anyway, but when it all works out....gorgeous results, I'm thinking seriously about a DP3M as well now that the price are seriously low.
Kind Regards, Sander