JSON_KEYS fails to deduplicate the same key when formatting the data with utf8mb4

SET @plain_dup='{"a":1,"a":2}';

SET @escaped_quote_dup=CONVERT(X'7B22615C2262223A312C22615C2262223A327D' USING utf8mb4);

SELECT JSON_KEYS(@plain_dup) AS plain_keys,

       JSON_LENGTH(JSON_KEYS(@plain_dup)) AS plain_key_count; -- ["a"]   1, this is correct

SELECT JSON_KEYS(@escaped_quote_dup) AS escaped_quote_keys,

       JSON_LENGTH(JSON_KEYS(@escaped_quote_dup)) AS escaped_quote_key_count; -- ["a\"b", "a\"b"]        2, JSON_KEYS fails to deduplicate this