At the Vietnamese Wiktionary, searching for “trường hộp” redirects to “trường hợp”, which is incorrect and potentially confusing to readers (because they might not notice the circumflex being replaced by a horn). At Vietnamese wikis, the search engine should perform case folding only for search suggestions, results, and Did You Mean; it should never redirect the user to a page that only matches due to case-folding. (There is one case where this behavior is useful: things like “xóa” and “xoá” are interchangeable. But we already have redirect pages for all these cases.)
The impact on Vietnamese wikis is high because most words have completely unrelated lookalikes when ignoring diacritics.