Death Items Swap

What I expected to happen was...:
I was Killing the Wither and on last hit he defeated me too i ran back in End to pick up my Items

What actually happened was...:
I was at my Death Point and found the Netherstar but my items where gone and replaced with items from my Shulkerbox i had in my Inventory

Steps to Reproduce:
1.Take a Shulker Box with items  

2.Spawn an Wither in the end 
3. Wither must be Half life
4. Let the Wither kill you not through the Wither Effect only through the Skulls