SUMMARY When setting the panel to be Opaque, some applets like Volume or Network will render their background with opacity whereas other applets like Kickoff or Calendar will render it opaque STEPS TO REPRODUCE 1. Set panel opacity to Opaque 2. Open Volume applet: background has opacity 3. Open Calendar applet: background is opaque OBSERVED RESULT Inconsistent applet background behaviour: some with opacity, some are opaque EXPECTED RESULT All applets should render the background by using the same style. Opaque in this case since it was the one selected for the panel SOFTWARE/OS VERSIONS Windows: macOS: Linux/KDE Plasma: (available in About System) KDE Plasma Version: KDE Frameworks Version: Qt Version: ADDITIONAL INFORMATION
Can confirm.
Ah, there's already a bug report for this: Bug 439025. *** This bug has been marked as a duplicate of bug 439025 ***