SOLVED:
Solution above doesn't work.
You need to open administrator/components/com_communityanswers/models/config.php
Find this line, should be line 46
$filtered_keywords = JRequest::getVar(FILTERED_KEYWORDS, 'blah,blah,blah', 'post','CMD');
and change it to
$filtered_keywords = JRequest::getVar(FILTERED_KEYWORDS, 'blah,blah,blah', 'post','STRING');
Then go to config area and input words to exclude again