I am not 100% sure on this but as a decision was made to defer the mandatory effective date of IFRS 9 from 1 January 2013 to 1 January 2015 I would think it is acceptable to refer to IAS 39 still in 2012 exams. As long as you apply it correctly I can see it being wrong.
IAS 39 is still being used by most firms hence can be used in the June exam. Since IFRS 9 has been publishd there is no harm in applying it to a question in the exam infact if u use IFRS 9 and apply it correctly as it shud b used u will sho th examiner tht u knw wat yo stuff, 1st January 2013 is jst th final date of adoption and early adoption is still an option. Bottom line u cn use eitha of th 2. Hop I hav helpd.