Incorrect assumption of full inventory with offhand

When your inventory is full with any item and you have arrows in your offhand, attempting to pick up more arrows will not work until you free up a slot in your inventory.   

  

Steps for reproduction:  

1. Put an arrow in your offhand, and drop an arrow on the ground  
2. Fill every other inventory slot with items besides arrows
3. If in creative, switch to survival
4. Attempt to pick up the arrow

What should happen: The arrow is picked up, and goes to your offhand

What happens instead: You are unable to pick up the arrow until a slot in your inventory is free. One you have a free slot in your inventory the arrow is picked up, and goes to your offhand.