Index: modules/overlay/overlay-parent.js
===================================================================
RCS file: /cvs/drupal/drupal/modules/overlay/overlay-parent.js,v
retrieving revision 1.11
diff -u -r1.11 overlay-parent.js
--- modules/overlay/overlay-parent.js	25 Dec 2009 10:15:23 -0000	1.11
+++ modules/overlay/overlay-parent.js	31 Dec 2009 10:44:14 -0000
@@ -413,6 +413,15 @@
   // Make sure the parent window URL matches the child window URL.
   self.syncChildLocation(iframeWindow.document.location);
 
+  // Unbind the mousedown handler installed by ui.dialog itself.
+  // The handler disables the vertical scroll bar in Chrome & Safari.
+  // After unbinding from the document we bind a handler to the dialog overlay
+  // which returns false to prevent event bubbling.
+  // @see http://dev.jqueryui.com/ticket/4671
+  // @see https://bugs.webkit.org/show_bug.cgi?id=19033
+  $(document).unbind('mousedown.dialog-overlay');
+  $('.ui-widget-overlay').bind('mousedown.dialog-overlay', function (){return false;});
+
   // Reset the scroll to the top of the window so that the overlay is visible again.
   window.scrollTo(0, 0);