Not an isolated incident, as different examination boards (including Cambridge) are behind the different erroneous papers.
http://www.bbc.co.uk/news/uk-13711599
http://www.bbc.co.uk/news/education-13703441
http://www.bbc.co.uk/news/uk-northern-ireland-11060872
LOL at first video
"Exams are bad enough without the questions being wrong as well" :)
I would also like to add that in exams, do not expect questions to be always correct, although the probability of it being wrong is low.
When answering questions, try to understand what the examiners want to know, even if you don't fully understand the question. Answer to give them what they want to ask and know, and scores will come your way.