Discussion on this topic at Meta.Math seems to suggest to me that quoted exact phrases will not match an exact phrase search. More precisely, the problem seems to be that searching for
will match the text
in the body or in the title, but not
(with the quotes added) in the body or in the title. For example, compare this output with this one. One would expect the first two results in the first search by also found by the second search. But that is not the case.
This is a bug that should be fixed.