When firing tipped arrows held in off hand bow fires normal arrows. If the arrows are placed in inventory they fire as tipped arrows with effect.
Bow is enchanted with:
Power IV, Infinity, Fire, Punch II, and Unbreaking III
Also, tipped arrow in off hand is not consumed, at first I thought it was a bug that was allowing infinite tipped arrows, but I fired at wall and noticed there was no effect particles from bow.