Exact same happened to me. Revenue have applied the amount to 2007 because they received details of my contribution in November, and would not consider the fact that it was received by the PRSA provider in October. They informed me that if I want to do this, I would have had to inform them prior to Oct 31 that I will be applying for back-dated tax relief.
Rang the PRSA provider - the first person told me she had Eur 2 million worth of claims still to be processed for 2006, and there should be no problem. Her superior confirmed that in theory the Revenue should be informed prior to Oct 31.