MB: So far as my A-levels went, the opposite was the case. For history questions were relatively predictable because to write history essays you need a basis of knowledge, producing a range of questions severly limited by how much candidates could be expected to know. Further Maths, on the other hand, used a fairly well known range of tools but a variety of different techniques, combined in infinitely many ways. It was damn near impossible to predict precisely which specific technique you'd need to apply and how.
At Oxford it's a bit different. One of my papers I knew the questions before hand, one I had absolutely no idea, and couldn't have written a paragraph on 50% of the question on the paper. It just depends on the specification.