Fulltext search in Mysql - illogical behaviour

I'm getting results that are hard to understand. I hope that someone will be able to shade some light on the subject.

I have a very simple table in mysql:

id| text
1 | testA testB testC
2 | testA testB

When I run the following query:

SELECT id,  MATCH (text) AGAINST ('+(+testA testB) +testC' IN BOOLEAN MODE) as score FROM test_fulltext 

I get the following incorrect results (note that the second row should return 0)

id| score
1 | 1,1666667461395
2 | 0,66666668653488

However when I run as slightly modified version of the query (no '+' sign before testA):

SELECT id,开发者_JS百科  MATCH (text) AGAINST ('+(testA testB) +testC' IN BOOLEAN MODE) as score FROM test_fulltext 

I get correct result:

id| score
1 | 1,3333333730698
2 | 0

Do you have any idea why the first query matches the second row? It does that on both mysql 4.1 and 5.0.5.

Do you know where I can find the source code that parses full text queries? Or any other source of information that explains how this is calculated. Any help is welcome.

It seems that it is a known bug that is present in all versions of mysql. http://bugs.mysql.com/bug.php?id=36384

You can check out the offical doc :

http://dev.mysql.com/doc/refman/5.0/en/fulltext-boolean.html