For example, when on lock screen and move mouse through the "Unlock" button, the screen blinks to black. When showing dialogue of confirming shutdown/restart/logout, the dialogue blinks to disappear. And when having progress on notification (like copying large files in Dolphin), the panel blinks. I'm not sure if it is a bug of Qt, but since this problem doesn't present on other KDE programs, I post this here. Reproducible: Always
Got fixed after upgrading Qt. So it's a bug of Qt, not KDE. Sorry for interfering.