Sliding menu is jumping?

I have used a basic jquery script to get the menu on my site to slide down and up.

When you click on the show/hide menu button, there is a little flash (Not a major issue) but when you close the slider, the page jumps up a little.

It looks a little glitchy?

http://designingthemes.tumblr.com/

Any ideas how I can fix that?

This is the code I am using

$(document).ready(function(){
$(".flip").click(function(){
    $(".panel").slideToggle("slow");
  });
});

Thanks.

Sorry, I have found a solution to this. I moved the div containing the slider out of the wrapper and have it across the top of the page. Seems to work great outside the wrapping div.