UTF-8 notoriously doesn't prevent ambiguous encoding by construction, but only prohibiting it in the specs. It's known as overlong encoding. It's up to the encoder/decoder to prevent, correct, or reject it. This burden on the software is exactly what TFA tries to eliminate with the bijou64 format (unfortunately replacing it with another burden: overflow check).
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UTF-8 notoriously doesn't prevent ambiguous encoding by construction, but only prohibiting it in the specs. It's known as overlong encoding. It's up to the encoder/decoder to prevent, correct, or reject it. This burden on the software is exactly what TFA tries to eliminate with the bijou64 format (unfortunately replacing it with another burden: overflow check).