Why does this filter not work

I try to clean up my comp.lang.python. For this I call:
    applyfilter comp.lang.python

One of my filters is:
    ^Subject:.*[ _]NAZISTA[ _]

There is a message which contains:
    Subject: PUTTANA NAZISTA MONICA LONGERI

So I would expect this message to be filtered, but it is not. What is going
wrong here?

-- 
Cecil Westerhof