Breaking a shulker box drops items

Breaking a shulker box with items in it drops the items

What I expected to happen was...:

to retain the items after breaking the shulker box

What actually happened was...:

breaking the shulker box with items in it drops the items, does not retain items

Steps to Reproduce:
1. I put the items in a regular shulker box
2. I broke the shulker box with items in it
3. It dropped the items from the shulker box without retaining it