He links to a stack overflow question and I think this answer is pretty good https://stackoverflow.com/a/23195243/497116.

https://www.ietf.org/rfc/rfc4627.txt says "The names within an object SHOULD be unique". https://tools.ietf.org/html/rfc7159 is more lax and instead says "An object whose names are all unique is interoperable in the sense that all software implementations receiving that object will agree on the name-value mappings". It's unfortunate that the correct behavior is not agreed on and today we saw the consequences of that.