Thanks for checking :)
I did the test with no pets, elixirs, buffs and with same gear equipped.
I tried it again just now, the % added for armor passive looks correct today. May be the issue is/was intermittent, but 15% Armor from Orc Shaman Effigy buff is still a little off, please see below:
Stats w/o Passive or Buff:
3427 Armor
Attachment 165564
Stats with Armor passive:
+5% Armor= 3599 (round off)
Attachment 165570
Stats with Orc Effigy Buff
+15% Armor= 4139 (round off)
Attachment 165569
As you see, the buff is only adding around 9.5% armor to the stat, off by around 198 armor.