When you select an option in screen configuration applet there is no persistent effect that provides the user for future usage which option is currently used. Each time you open the applet none of the five options appears selected. This is very important to troubleshoot any problem with cables/external monitors, so it's useful that Plasma desktop through its screen configuration applet could provide the user which screen mode is currently selected.
*** Bug 474158 has been marked as a duplicate of this bug. ***
So this UI isn't designed to show you the current mode; it's a set of quick actions to change the mode to something else. There are many more modes that you can be in which can't be represented by these simple settings. if your current mode does in fact match one of the pre-set ones, we could make it highlight that. But the moment you change it, it will have to stop highlighting it.
(In reply to Nate Graham from comment #2) > There are many more modes that > you can be in which can't be represented by these simple settings. I think those 5 standard options are enough for normal usage, even Windows only provides 4 generic choices. > if your current mode does in fact match one of the pre-set ones, we could > make it highlight that. But the moment you change it, it will have to stop > highlighting it. This will help users to identify the source of problems for example when they do their presentations, because from experience the most known cause is those faulty old cables, so knowing that the correct display mode is already selected in Plasma desktop is a plus, similarly to how Windows highlights the current used mode.