hmm ... adding a few rows not matching the word seems to help in my test DB. Now I found out how the 50% rule works.
INSERT INTO `matchtest` VALUES ('5', 'nofind 1', 'nothing');
INSERT INTO `matchtest` VALUES ('6', 'nofind 2', 'old as stone');
INSERT INTO `matchtest` VALUES ('7', 'nofind 3'...