The anvil character limit is too short. The block "Waxed Weathered Cut Copper Stairs" has the longest name. But it's impossible to input that many characters in an anvil.

How to reproduce:
Get an anvil
Rename something to the maximum character limit
Compare it with "Waxed Weathered Cut Copper Stairs"

What I expected:
The characters will be long enough to match "Waxed Weathered Cut Copper Stairs"

What I saw:
The characters are less long than "Waxed Weathered Cut Copper Stairs".