zIndex failure in multiple dialogs

zIndex failure in multiple dialogs

I use two dialogs the first using the second

  1.     unionDialog = $("#setUnion").dialog({
  2.          autoOpen: true,
  3.          /* modal: true,  */
  4.          zIndex: 500,
  5.         position: [75, 50],
  6.         width: 750,
  7.        });

  1.   Calendrier = $('#calendrierGeneral').dialog({
  2.          autoOpen: true,
  3.           /*modal: true,*/
  4.         width: 450,
  5.         zIndex: 1000,
  6.        });
In fact the first (actually called for some reasons after the second) opens with z-ndex = 1002  and the second with z-index = 1001.
Then the first masks the second ( even more absolutely with "modal = true" )
Notice than my "zIndex" is not zindex

How can I fix z-index ?