And regarding the actual header message, this is controlled by amavisd-new, not spamassassin, and was implemented in amavisd-new 2.6.2 See
[...]the score used to trigger autolearning is somewhat different than the one reported in the final score; therefore a score displayed in the headers that obstensibly should trigger autolearning will not do so. Again, use the "-D" flag to SpamAssassin, and you will see the score that is used to determine whether or not autolearning will be triggered.
Finally, SpamAssassin requires at least 3 points from the header and 3 points from the body, to auto-learn as spam. If either section contributes fewer points, the message will not be auto-learned.