In installs using MySQL 5, I've noticed that when adding double quotes to the search term (as per the instructions: to search for an exact phrase, enclose the phrase in quotes), in the search results the double quotes get encoded to " and display as " rather than ".
As an example: when searching "sample phrase", the result would be:
You searched for... "sample phrase".
Reported on Movable Type 4.2

Let's try that again without the garbled code:
Damn - third time lucky, perhaps.
And if the preview worked better we wouldn't have this malarkey.
In the returned result, instead of "sample phrase", the double quotes are replaced with ampersand+quot+semicolon.
In init.fastsearch.php, replacing
$string = str_replace( '\"', '"', $string );
with
$string = str_replace( '\"', '"', $string );
now returns " rather than " in the results and appears to fix the issue.
With minimal knowledge of this stuff, I'm assuming this is something to do with things being printed rather than evaluated (and vice-versa).