The problem is that the 'default ui settings' button is directly below the list of skins. when you click one it takes several minutes to load and looks like the game froze so if you click again you are actually clicking the default button and resetting your UI options. When I first did that it took me about 3 days to even notice that everybody's names were different colors and I couldn't understand why my ranger would grab his cure wand every time I tried to sneak . Maybe they can add a timer to prevent any changes for 30 seconds or so after changing a skin, or move the default settings button
So far the only time I've had trouble with the 'none' skin not all changing back was when I had errors in the SkinDefinition file or missing images.