I have noticed this interesting behavior several times now.
Many a time I scour Math SE looking for a particular query but fail to find anything even after several rounds of rephrasing and reformatting my query. I finally accept defeat and decide to ask a question myself, so I type in my question title and lo and behold! there are one or two relevant results under "Questions that may already have your answer". But then pasting and searching for same title text(equation markup included) yields no results.
So if Math SE has the ability to do a better markup-aware search feature which can return more relevant results, why is it not implemented for the normal search function? Is it an issue of computational cost?