I tried the workaround that Troy R. proposed already some time ago but it didn't help - the option 'Nothing' then also appears as on option under Power Management Preferences but the behaviour is still the same as 'Blank screen' would have been selected.
I tried the workaround that Troy R. proposed already some time ago but it didn't help - the option 'Nothing' then also appears as on option under Power Management Preferences but the behaviour is still the same as 'Blank screen' would have been selected.