If you use "Find Messages" in KMail and chose "Match any of the following" you don't get the expected results if you add one more criteria with More.

e.g. You search for the first criteria "Subject contains test" and the second "Subject contains test2". Then it works right and will display all the messages which contain one of the two words.
If you now add another criteria with More, lets say "Subject contains test3", you won't get the expected result of displaying all the messages with contains either test, test2 or test3 in the subject. It works like only the last two criteria types work with an AND conjunction.