Maybe the control panel displays the requested aperture, while the viewfinder displays the actual aperture. Let's say you have an f/4 to f/5.6 lens: You dial in f/4 at 18mm but then zoom in to 150mm, where the lens can only go to f/5.6. So the viewfinder displays the actual f/5.6 the lens is delivering, while the control panel still displays the f/4 you have requested (and which you will get as soon as you zoom out again or swap to a faster lens).
If so, then it seems a sensible way to arrange things. My Canon does it the other way (i.e., in the example above, both displays will read f/5.6), which sometimes leaves me unsure what requested aperture I have set. I wouldn't mind it the other way around either. Not sue that it matters much.
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