Dialog "System settings" -> "Display and monitor" -> tab "Display configuration". Check box to enable/disable monitor and "star" button to toggle primary output has same x, y position. User can't toggle check box, because "star" button cover it. Reproducible: Always
Could you please add a screen shot showing the issue? It looks correct here.
Created attachment 86905 [details] Screenshot with bug demonstration
We redesigned the UI in Plasma 5, moving all controls out from the tiny boxes that represent screens, so this won't happen anymore.