[JS] - Menu System

I am redesigning a site and I have this menu system from a previous project that i used again to fit this project.
In this website it is used in the left nav: http://www.uthouston.edu/worklife
Now i am using it here in the roster: http://www.kleinoakfootball.com/teams/varsity/roster.php

My question is, when you click one item, then click another, when it collapses the open item and expands the item you just clicked. The problem is, all the items below the item you just clicked move down a little and then up. Its almost like they are moving at slightly different speeds.

What is causing this and how do i prevent this from happening so that the items below the one clicked dont move at all?

here is my JS: http://www.kleinoakfootball.com/sdmenu.js