You ARE picking up items, but it doesn't update correctly. Resulting running out of items from your hand.

Both main and off hand have same problem.

Reproduce:

1. have full stack in hand.
2. be around same item sitting on the ground.
3. consume items in your hand and picking up items from the ground.
4. running out of items in your hand.
   1. open inventory and click on the slot to update it correctly.