So after my defect report (H4OS-9935 The Fader Option of 'Flash at Full' acts like 'Flash at' after a show file export/import) was fixed at v4.2, it seems that something else might got broken by that.
Usually real world values seen in the output window get translated to DMX values after that stage. I noticed that with v4.2 when pressing a group masters flash at full button the intensity value is translated from percent to DMX scale in the output window stage already, so that for example it is possible to have 255% Intensity. This values are then again translated correctly to DMX values, which leads to problem, that e.g. 25% intensity gets 63% in the output window and 161 as DMX value, which leads to much greater brightness of a fixture than intended and programmed.
Switching to "flash fader at 100%" helped me to get along with the show tonight, as that works as expected, but it would be cool if that could be fixed.
Thanks a lot. :-)