Screenshot of problem:
A similar issue (T30318) was filed in the past and resolved.
It appears to be back.
Once again (or still), the dialog has a custom spinner that:
- has a fixed white background (causing it to stand out against the grey background of the dialog for no good reason)
- doesn't look like other spinners used in MediaWiki (circulating blue dots instead of black lines).
Should probably use the code spinner icon instead.
See Also: T61699