nUI does not interact with any of Blizz's built in frames like spellbook, talents, etc. I won't say that there isn't some oddball bug that might cause that, but I would be flabbergasted if nUI had anything to do with this problem... it does not alter those panels in any way and does not interact with the code that drives those panels. I would say with 99.9% certainty it has nothing to do with nUI.
What people don't get is that I am, ultimately, an artist at heart. My brush has two colors, 1 and 0, and my canvas is made of silicon.