SUMMARY I found this because I have a plugin that sets the brush size, but was able to reproduce with the Scripter plugin. STEPS TO REPRODUCE 1. Open Scripter plugin, paste: win = Krita.instance().activeWindow() view = win.activeView() view.setBrushSize(5) 2. Open brush editor (in detached mode). 3. Run script. OBSERVED RESULT Note that the brush size changes in the toolbar but not the brush editor. Changing anything in the brush editor causes the size to reset to what the brush editor thinks it is. This also happens with opacity (setPaintingOpacity) and I'm guessing anything else that can be set via the API. EXPECTED RESULT Changes are "applied" everywhere. SOFTWARE/OS VERSIONS Windows 10 Krita Nightly 4407898
Related to https://bugs.kde.org/show_bug.cgi?id=435502
Seeing that other bug report, it looks more like the bug is the brush editor was never designed to "listen" to external changes since it didn't need to be, although strange the sliders do affect it. Did not think to test this at the time, but any changes that can be made via the popup palette brush hud are also a problem.
Remove triaged keyword from CONFIRMED bugs