Steps to reproduce:
- Go to https://en.wikipedia.org/wiki/Special:ApiSandbox.
- Select action=query, change to that page.
- Enable prop, type "c", select "categories" from the list.
Alternatively, in step 3 you can type "categories" and press enter, without using the list.
Expected: Input is valid, so it shouldn't be flagged.
Actual: Border and cursor are red, indicating an invalid input.
Removing the focus from the input fixes the display (until the next time you enter something via keyboard), but shouldn't be necessary.