The Shield Defense Feat (Guardian Fighter, Protector tree, 2nd tier) states that it gives 1/2/3/4/5 AC. However, after the 1st point invested, it still gives only 1 AC. This has been tested both with 2 and 3 points invested in the Feat. Both the AC score in the character sheet, as well as the damage reduction, remain the same when investing additional points after the 1st.
Comments
http://nw-forum.perfectworld.com/showthread.php?180181-Guardian-Fighter-Feat-Bugs