I renamed an Orange Shulker Box as "Valuables" first, then later reproduced this bug with a Blue Shulker Box named "Tools/Equipment."
Both instances showed signs of this bug.

What I expected to happen was...:
I expected the Shulker Box to have the name I renamed it to with the anvil show up as the label in the GUI

What actually happened was...:
The GUI still listed it as Shulker Box instead of the name I gave it

Steps to Reproduce:
1. Grab a Shulker Box and an Anvil
2. Place the anvil and re-name the Shulker Box to anything of your choice
3. Place the renamed Shulker Box anywhere and open it