I think reading while you are already working on the problem could be helpful in both directions. On the one hand, while reading you will be more alert to stuff that might be useful for solving the problem, so you will have better chance of paying attention to it. On the other hand, if you already have a problem in mind and you are trying to see how to use the stuff that you are learning to solve the problem, then your learning process is more active and your understanding of the material will be better (or at least some aspects of it).