I used to be able to hit the tab key and it would jump to the color correction fields (temp & tint), and each time I tabbed it would go down the right side through the exposure and other corrections. So in 3 tabs, I would be to Exposure.
I changed nothing. Now it jumps through the all the buttons like preview, shadows, highlights and the workflow options at the bottom. It doesn't highlight exposure like it used to.
You probably accidently hit the Control F7 keycombination. Hit it again and you will return to the normal behavior.
See also the System preferences Keyboard and mouse. In the Keycombination section at the bottom of the window are 2 radio buttons that change with the Ctrl F7 combination. In the settings field you can disable this with uncheck.