When a KCModule is loaded that is too high, it won't get scroll bars when loaded in kcmshell5. System Settings adds scroll bars around it. Reproducible: Always
For example in right click on 'Battery and Brightness' widget -> 'Configure Power Saving...' -> 'Energy Saving' window is on fitting vertically on 1366x768 screen.
*** This bug has been marked as a duplicate of bug 366299 ***