yeah that's exactly what I'm saying about the x and y's. I have only found it usefull with "ToolbarField" tag tho.
If you edit anything under "ID_UISkin_Toolbar" the clipping takes place while switching modes, there's no way around it, at least I haven't figured out one. Not sure if you leave the values blank which you don't need to modify what happens then, I can't remember if I tried that, I think I did but not sure anymore .. been a long while since I messed with that part of the code. It would be ok if you wouldn't need to include "ToolbarField" but as it's the parent tag you can't leave it out.
Oh and remember that when you modify the code you can leave out any child tags you don't modify, the lotro ui will fill out the blanks automatically.
I don't mind the bug myself as im always alt+tab'ing instead of switching between fullscreen/windowed mode. That doesn't affect the skin.