GROUP BY with GROUP_CONCAT breaks BIT field in MyISAM

SELECT  PARTYID, ACCEPTED, GROUP_CONCAT(ASSOCID) AS ORGIDS

FROM party_test

LEFT JOIN connect_test

       ON MAINTYPE = "party"

      AND MAINID = PARTYID

      AND ASSOCTYPE = "organization"

WHERE STAMP BETWEEN 1683277200 AND 1683363600

GROUP BY PARTYID

ORDER BY PARTYID;

SELECT  PARTYID, ACCEPTED, ASSOCID AS ORGID

FROM party_test

LEFT JOIN connect_test

       ON MAINTYPE = "party"

      AND MAINID = PARTYID

      AND ASSOCTYPE = "organization"

WHERE STAMP BETWEEN 1683277200 AND 1683363600

ORDER BY PARTYID;

+---------+----------+----------------------------+

| PARTYID | ACCEPTED | ORGIDS                     |

+---------+----------+----------------------------+

|  430921 |          | NULL                       |

|  436261 |         | NULL                       |

 +---------+----------+----------------------------+

+---------+----------+-------+

| PARTYID | ACCEPTED | ORGID |

+---------+----------+-------+

|  430921 |          |  NULL |

|  436261 |          |  NULL |

+---------+----------+-------+