Hi AMC
This is both a technical limitation and a feature, depending on how you see it.
I don't want to go into deep technical details, but basically to be able to sort kanji and kana, romaji has to be case-sensitive.
Taking the same example that you provided, I also think that it's not the same to search for "man" than to search for "MAN". The second is normally used for acronyms rather than "normal" words, so if you ask me, it's better to have different search results, as the more relevant ones are the one that are in uppercase.