Impossible to rename items using anvils in snapshot 17w47b

Steps to recreate:
-Put a default item in an anvil and try to rename it
-Click on the output
-Observe that the item reverts immediately back to the input slot, unnamed

Putting an already custom named item given using commands in the input slot of the anvil will also fail, but instead the item will appear in the output and revert back to its default name.