@cmh: Thank's for the reply.
Meanwhile I got rid of the issue with a fresh reinstall of magiclantern-Nightly.2018Jul03.EOSM202 to the SD card.
Because I had tested another very experimental build on the same SD card before, my assumption is that some config stuff was left over that conflicts with the nightly build. But I don't have a proof for that and the shutter bug thing might be a root cause too.
Meanwhile I got rid of the issue with a fresh reinstall of magiclantern-Nightly.2018Jul03.EOSM202 to the SD card.
Because I had tested another very experimental build on the same SD card before, my assumption is that some config stuff was left over that conflicts with the nightly build. But I don't have a proof for that and the shutter bug thing might be a root cause too.