Repeating the last number when updating in a stored procedure

CREATE DEFINER=`root`@`localhost` PROCEDURE `SampleProc`( name_in INT)
BEGIN
DECLARE exit_loop BOOLEAN;
    DECLARE l_name INT;
            DECLARE X  INT;
     DECLARE Y INT;
     DECLARE c1id INT;
      DECLARE done INT DEFAULT FALSE;
        DECLARE cur CURSOR FOR SELECT PaperID FROM scrpd_paper_authors WHERE AuthorID=name_in;
     DECLARE cur1 CURSOR FOR SELECT AuthorID FROM scrpd_paper_authors WHERE PaperID=l_name;
     DECLARE CONTINUE HANDLER FOR NOT FOUND SET exit_loop = TRUE;
    OPEN cur;

     example_loop: LOOP
      FETCH cur INTO l_name;
      IF exit_loop THEN
    CLOSE cur;
    LEAVE example_loop;
    END IF;
    OPEN cur1;
      example_loop1:LOOP
       FETCH cur1 INTO c1id;

    UPDATE recipes_new SET co_auths = IF(LENGTH(co_auths), CONCAT(co_auths, ',', c1id), c1id) WHERE id = name_in;       

       IF exit_loop THEN
    CLOSE cur1;
    LEAVE example_loop1;
     END IF;
 END LOOP example_loop1;
 END LOOP example_loop;
END$$

I made a stored procedure in sqlyog, the problem I ran into is that when I see the results in the table after the update has been done, it is 1,2,3,3, whereas it should be 1,2 , 3 last record is repeated. Any guesses what the problem is?

recipes_new(My current result)       scrpd_paper_authors

id     co_auths                      PaperID     AuthorID

====    ========                      =======     ========
 1          1,1                          1            1
 2          2,2                          2            2
 3          3,4,4                        3            3
 4          3,4,5,6,7,7                  3            4
                                         4            5
                                         4            6
                                         4            7

as you can see in recipes_new (My current result), getting extra numbers at the end. My expected result

 1
 2
 3,4
 3,4,5,6,7