There seems to be a problem with the creation of spam filter rules. Here's what's happening:
I enter one rule for "Title" and "contains" with "rule1" for the criteria.
I enter another rule for "Title" and "does not contain" with "rule2" for the criteria.
When I add that second rule, it overwrites the first one, creating a rule for "Title" and "does not contain" with both "rule1" and "rule2" as its criteria. I really hope this is not a limitation, because I need to be able to set multiple rules based on the Title field of incoming emails.