No button icons are shown for most buttons in Window Decoration settings. Reproducible: Always Steps to Reproduce: 1. Open System Settings 2. Go to Application Style->Window Decorations->Buttons Actual Results: Most icons for buttons missing, and when you try dragging the text, you miss when trying to place it on the "Titlebar" part of the widget, because the button's symbol which appears above the dragged text is almost invisible, and the text itself seems to not be a valid object to place. Expected Results: All buttons, not just Menu and Close ones, should be visible — at least some placeholders for them, if no icons are available.
Created attachment 99450 [details] Screenshot
do you have breeze installed?
i think I do: it's the default decoration on Kubuntu. In the list of decorations it's called "org.kde.breeze".
icon theme, not decoration. looks like you're using oxygen and neither it nor it's inheritence provide the icons. nevertheless, the items should probably work regardless of the icon theme (ie. display a square or some ugly internal failsafes)
I do have Breeze icon theme, but even selecting it as current theme doesn't show the windeco button icons, although all other icons do change.
did you restart systemsettings after changing the theme?
Yes, I restarted it. In fact, even without restart the menu icon had changed to Breeze version of it. But the others except "close" still remain invisible.
I've checked this on live image of Kubuntu 16.04, and it doesn't show this bug. Apparently this is a buggy upgrade process, which led to this, not a problem with KWin itself.