Submenu navbar: it opens late and shows different background

I installed Drupal 7.12 and Superfish module v1.9.b4 with its libraries and set mode Navbar. I noticed that the submenu does not open immediately, but with a fraction of a second too late, when I move the mouse between the various menu items. At mouseout, moving between a menu item and the other, submenu disappears and then reappears, all in less than one second. It creates an annoying effect that I would like to delete. See below!

Here (in "Example"> nav-bar style) an example of how I want it to be:
http://users.tpg.com.au/j_birch/plugins/superfish/ # sample4

Here you can check the menu:
http://www.tusciarealestate.eu/node/3

Can you help me to solve the problem?