When using touch and System Settings is small enough as to merge the category panes (e.g. the one where Workspace behavior lies and the one where General behavior lies), one touch on top of the button to switch between panes isn't enough for the action to complete; you need to touch the arrow to return. This works if you advance, though.

The only other way you can switch between panes is by swiping, but that's not intuitive at all, so it shouldn't be the default experience.

It's a bit confusing, so let me exemplify:

System Settings window is as small as can be, so both panes are merged.
First pane contains things like Appearance, Workspace behavior, Window management, Shortcuts, Startup and shutdown, Search, etc.
Second pane in Search contains things like File search, KRunner, Web search keywords.

- You're on the first pane and you touch anywhere in the Search button except the arrow, it advances to the second pane.

- You're on the first pane and you touch the arrow in the Search button, it advances to the second pane.

- You're on the second pane and you touch anywhere in the Search button except the arrow, it DOES NOT return to the first pane.  <---- This is the bug

- You're on the second pane and you touch the arrow in the Search button, it returns to the first pane.

While swiping works and it serves as a workaround for this issue, being unable to return to the previous pane by pressing anywhere in the button is still an inconsistency bug.