SQL query not returning the value expected !!!!!!!!!!!!!!!!!!

Hi if you take a look at the following query's you can see that the third query should logically return 043219
but instead it's not returning any rows ?? What's happening ??????????????

dragon=> SELECT cod_etu from parcours_v where cod_etu = '043219';
cod_etu
---------
(0 rows)

dragon=> SELECT cod_etu from parcours_hors_cursus_v where cod_etu = '043219';
cod_etu
---------
043219
(1 row)

dragon=> SELECT cod_etu from parcours_hors_cursus_v where cod_etu ='043219' and cod_etu not in (select cod_etu from parcours_v);
cod_etu
---------
(0 rows)