i know you should probably look at the past papers, or as many as you can. But seeing as the past papers you are looking at are not to do with this years exams, stop looking and don't give your self the headache. 2008 was still the paper based exams and they cover more than you need to for BA1. Speaking of which control accounts are not really covered until BA2. Going through as many of the practice questions and the two exams on here should be enough to help you get an idea of what the exam will be like, but try and stick to the ones based on the last couple of years exams, purely because at least then you are only testing yourself on what you have actually covered!
But to answer the question your asking, i think that the exam is wrong...lol unless anyone else can think of a reason that the Purchase Ledger Control account would have a debit balance?
Month End is approaching - Keep Calm and Carry on Accounting