Unwanted yoyo effect on slideDown/slideUp

Unwanted yoyo effect on slideDown/slideUp

I am trying to make a menu that has a rollover which displays an image on top and is revaled sliding down from top to bottom. I want the rollover image to dissapear when rolled off the button by sliding back up.

This is where I have got so far:
http://exsiteinteractive.ca/yoyo/yoyo.html

Problem here is that when I rollover i am getting a yoyo effect but i want the hover image to stay down until rolled off the button.

Based my code around this:
http://www.webdesignerwall.com/demo/jquery/animated-hover1.html

Please Help.