"Object keys must be unique.""

How should the following be serialized (if at all)?

{"a":0,"\u0073\u0323\u0307":1,"\u1E69":2,"Z":3}

Note that I'm using the \u forms even though they aren't allowed via the specification because, HN doesn't show unicode combining properly sometimes, and so that's it's clear to see that it's a different byte pattern.