This is a problem I've stumbled many times in Math.SE. When I want to ask something, I go to search to see if my question was already made, and most of the time I find nothing related. But then, when making a title on "Ask Question", the search there shows a lot of results that didn't appear on normal search, frequently showing me a previous question equivalent/related to mine. This isn't supposed to happen, I think, or maybe I'm not using the search system properly.
Example: 
