The menu on the page looks like you may be working on it currently as it was just a list instead of the links images like before.
As for the menu items disappearing this may have to do with the li losing it's focus when passing over it, the attention may be going to the background and causing the menu to collapse. I saw a post earlier from a user that was reporting a similar thing, they posted that they adjusted the widths of the menu and got it to not do this. Perhaps this is something you can try. let us know if you continue to have problems with this.