The short answer is to click the name of the Basic panel option you want to assign to the -/+ keys. In this case, click the Exposure text. A message should appear confirming this change.
It happened because those shortcuts were never tied to a specific control, but switchable. The idea was that if you were editing with the keyboard alone, like in Full Screen Preview, you could cycle through the options without having to exit Full Screen Preview. So, what probably happened is that the key that advances to the next or previous option was accidentally pressed, or at some point the Clarity option text was unintentionally clicked.
The way it’s designed to work is like this:
- Press - or + to adjust whichever option is active for that shortcut. (You know about this part.)
- To adjust a different option, press < or > to go to the previous or next Basic panel option. (You probably pressed one of those keys by mistake, and that cycled - / + to the next option.)