Sorry, was reading and saw this, thought I'd chime in for the first time
That is a known Blizzard issue at the moment. It has to do (I think) with the changes they made in part to the Sapphiron portal so it would not auto-port you after coming back from the final wing of Naxx. I could be wrong, and it's a due to something else entirely, but regardless: it's not nUI's problem.
EDIT: To clarify, I think it's a change to the detection of being in a "zone" where an action is taken on your character, either teleporting (as seen in Naxx) or changing your status to "Resting". In Naxx, you have to run off the blue field and back on to be ported to Sapph's chamber now (pre-3.0.9 it would auto-port you, not giving a chance for repairs, etc).
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Oh, btw- outstanding UI, Scott. I hope it stays around for a long time to come. Expect a donation from me soon as thanks for your hard work.