This is a problem which has happened many times when I want to ask a question on MSE. After I finish the title of my question, there'll be a Similar questions box to offer me some similar question. If I see some really similar question, I won't ask again to avoid duplicated work.
However, there's many times that I didn't see really similar question that can answer my problem after I finished my question and was going to post. But soon after I've already posted my question, the Related box at the right side of my question page will offer me some question that can really answer my problem. And my question becomes duplicated actually.
Why these two systems differ so much? I hope we can improve the Similar question box to behave like the Related box. The latter one performs better. In this way we can reduce duplicated work.