If there exists a redirect page for the exact search term, but also a non-redirect page with different capitalization, the latter is what you get when you put that term in the search box and press enter.
For example, on English Wikipedia, [[Koan]] is a redirect to [[Kōan]]. However, if I put "koan" into the search box and press enter, I end up at the page [[KOAN]]. If a redirect page that exactly matches the search input exists, this should always have a higher priority than a page with different capitalization.
(I been having frustrations with the way redirects are handled by search for a while now, but the precise problem never crystalized for me until now.)