I'm seeing problems with the wedges in this post, but not in simple cases like this one.
What would happen is that I'd click on a wedge, it wouldn't change. Then I click again, and the src attribute of the image would change to "undefined" in Firebug. Not sure what that means.
No, it still works.
In any case, in one of my calls to the expandCollapse routine, I omitted the values for urlExpand and urlCollapse. So when I click on the item to expand it the image goes undefined. Let's see what happens if I fix it.
Yep that was it.