Armor bonus from feats not applied until unequipping and re-equipping armor

At leveling up to level 4, I selected the feat that is supposed to add +1 to armor for every armor piece worn. However, this bonus didn't get applied until I removed the armor from my character and re-equipped it.

Side note: What actually counts as "armor piece" here? Shields don't seem to count. Does it only apply to the main body armor?