Yea, the UI is a really unorganized
After the release of DoF I they looked like they where in the process of changing how they organized things. WindowElements, CommonElements ect..
But with the coming release of EoF I notice they are adding stuff in random places. Some new things here and there that doesn't follow any pattern.
The best thing to do is look at the style property to find the style. Then you have to look at the style to see where it's getting it's images from. Kind of depressing they don't have a standard. I makes it a pita to make drop in skins. When 95% of the UI elements use things from a common place, then there is that 5% that use things from another place.