As reported by many readers (including Pen And tell and Denjw) the 4.2 firmware update for the E-M1 contains a major bug on. It locks down and creates corrupted images when using those functions:

– Focus Stacking

– Keystone

– HDR

– Starlight mode

So please do not install the firmware. Or if you already installed it don’t use those functions until Olympus will release a bug fix (hopefully soon).