In The Time of the Doctor:
When answering to the question what her name was while still being unaware of the truth field, Clara spurts out something, I couldn't make out even after several re-watches of both the original and the German dubbed version. But it definitely wasn't "Clara Oswin Oswald". It sounded more like a string of techno-babble or a machine designation.
I have read tons of reviews and am baffled that not a single one has picked up on this as it felt like one of the biggest mind-blowers in that episode for me.