For knights, the AC softcap increase on the type 18/19 Defense softcap augs does not work with a 2hander due to the Two-Handed Proficiency AA. It only works with sword and board. I understand the proficiency AA buff is supposed to negate the effects of combat stability, but is it also supposed to negate the effects of these defense softcap augs?
It's all SPA 259 and this AA negates it. So it's not a bug. It kind of places Combat Agility on a higher tier of value, while you're earning AA, if you want to use 2H while tanking. Purchase CA before CS in that case. I.e. why prioritize AA that is disabled by your favored mode of play?