Problem started to happen since I updated to 5.9.5. New windows and windows that were hidden and shown again appear on all desktops. Moving window to specific desktop only holds until the windows appears next time. Window title context menu always shows "show on all desktops" even if I selected specific desktop before.
please provide the output of: qdbus org.kde.KWin /KWin supportInformation Also please use xprop and xwininfo on a broken window.
Ok, my bad. Seems I haven't fully restarted system after major update. After I rebooted, the problem was gone.