Before it goes for service ...

Further investigation of yesterday's problem seems to show something on the sensor, not visible even with a magnifying glass. It is not where most of the problems occurred yesterday, so I think the bug is now dead, but lying on the sensor. However, I can't get it off the sensor using the (usually 100% reliable) auto mechanism on the Olympus, nor will a Visible Dust Blower move it. The E-M1 has a very sophisticated image-stabilised 'floating' sensor, so it would be stupid to try to remove this with a swab, so the camera is going to have to go back to Olympus for a sensor clean. Very depressing - it's only 2 months since it had to go back for service for a problem with the mother board/cabe connector, though of course this time it is in no way the fault of the camera.

In the meantime, I guess the E-M5's will take over for most of my serious photography.