I think it's about getting used to a system based purely on attack. The defenders are, in the main, good players. However some are used to playing as full backs, and so naturally get dragged wide. This happens more because the wide players are told to stay forward.
I think they seem to be starting to get to grips with it now, our wide players are defending properly higher up the pitch, allowing Raynes to keep the three together. Curle has created a good base, the players are learning on the job and we are improving rapidly.