The zIndex of a dialog's overlay should be one less than that of the dialog.

Author: PaulUithol

tests/unit/dialog/dialog_options.js

@@ -469,7 +469,7 @@ test("zIndex", function() {
 	// At the moment, an explicit zIndex option lower than $.ui.dialog.maxZ will be ignored since 'open' calls
 	// 'moveToTop'. Is this the desired behavior?
 	el = $('<div></div>').dialog({zIndex: 1584 });
-		equals(dlg().css('zIndex'), $.ui.dialog.maxZ, "explicit zIndex, lower than $.ui.dialog.maxZ, is ignored");
+		equals(dlg().css('zIndex'), $.ui.dialog.maxZ, "explicit zIndex at instantiation below $.ui.dialog.maxZ is ignored");
 	el.remove();
 });
 

ui/jquery.ui.dialog.js

@@ -602,15 +602,15 @@ $.widget("ui.dialog", {
 						$.ui.dialog.maxZ = value;
 
 						if ( self.overlay ) {
-							$.ui.dialog.maxZ += 1;
 							$.ui.dialog.overlay.maxZ = $.ui.dialog.maxZ;
+							$.ui.dialog.maxZ += 1;
 						}
 					}
 
 					value = $.ui.dialog.maxZ;
 				}
 
-				self.overlay && self.overlay.$el.css( "z-index", value > 0 ? value : 0 );
+				self.overlay && self.overlay.$el.css( "z-index", value - 1 );
 				uiDialog.css( "z-index", value );
 
 				break;