I found a bug from Armor Training & Tower shield Training on PS4

The version I play is kingmaker for PS4 sold in Japan.
When my Valerie reached lv3 tower shield specialist(aside from lv1 thug), I found that:
Even though I’m NOT equipping an Tower Shield or equipping a Heavy Shield, the Tower shield Training’s bonus in witch “the armor penalty is reduced by 3 and the maximum dexterity bonus allowed by tower shield increase by 2” is still active.
What’s more, it is actually reducing total armor check penalty from my Banded Mail from -6 to -2,and my Dexterity AC bonus apply as +3 when my off-hand is empty and my Fighter Class level is only 3.

Please kindly tell me if I overlooked something from the game mechanism or it is really a bug.