I fighted against a Shulker in the End.
I used a Bow as weapon which I had in right hand, 64 Arrows with the "Harming" effect in left hand.
I shot an arrow, but it don't hitted the Shuker, it flew away.
I followed it and picked it up.
Later I opened my Inventory and saw that there are 63 Arrows (Harming) in the left-hand-slot,and 64 Arrows (Harming too) in the Inventory.

My conclusion was;
I picked up 1 Effect-Arrow and I got 64.

What I expected to happen was...:
I thought I get one Arrow onto the 63 stacked Arrows in my left hand.

What actually happened was...:
Instead of I got 64 Arrows into my normal Inventory.

Steps to Reproduce:
1. Go into Survival Mode.
2. Get a bow into your Horbar.
3. Place 64 Arrows in your left hand.
4. Shot onto the ground.
5. Pick up the Arrow.
6. open your Inventory and see what happened.