In Krita 3.0.1.1, with a newly stamped brush tip, Clicking the "use color as mask" checkbox has no effect. The checkbox gets ticked, but as soon as you leave the brush editing window, it gets unchecked. Also, the brush tip still draws as an opaque black and white image. I moved the .gbr files to another computer running Krita 3.0, and was able to properly change the parameter, save a preset, and move it back to my main workstation. So this seems to be specific to 3.0.1.1.
Basically, no options that are placed below the preset chooser work and are reset on every editor opening :(
Git commit b46e7db264c8aaf111c89cbe2d3128f2d1041ca4 by Dmitry Kazakov. Committed on 18/10/2016 at 17:59. Pushed by dkazakov into branch 'master'. Fix the Predefined Brushes The problem is that we share a single KisBrush object across the entire Krita. Therefore, if we start writing into the settings object and some other code will get notifications that "something has changed", that other location may override some settings in the shared KisBrush. Therefore we will continue to write wrong values to the brush. Therefore now we postpone all the updates of the settings object until the entire write operation is completed. The postponing is implemented using a special KisPaintOpPreset::UpdatedPostponer class that uses the interface of updates proxy to do the stuff Fixes T3925 M +15 -0 libs/image/brushengine/kis_paintop_preset.cpp M +14 -0 libs/image/brushengine/kis_paintop_preset.h M +34 -2 libs/image/brushengine/kis_paintop_settings_update_proxy.cpp M +17 -0 libs/image/brushengine/kis_paintop_settings_update_proxy.h M +12 -1 libs/ui/kis_paintop_box.cc http://commits.kde.org/krita/b46e7db264c8aaf111c89cbe2d3128f2d1041ca4