Under a search of "ancestorIds:425988 AND test", the did you mean code will always say "Did you mean: ancestoring:425988 AND [Search Term]", which makes things more confusing since the user did not even add the ancestorIds bit to the search. It shouldn't change ancestorIds to ancestoring.

Workaround as suggested here:

1. Create an empty page with the page title ancestorIds
2. Goto your Confluence Administration
3. Goto Administration -> Content Indexing
4. Rebuild the "Did You Mean Index"