I don't think that any form of formal specification will solve that issue. The only way to minimize the impact of it is to work on small iterations (agile) and

I don't think that any form of formal specification will solve that issue. The only way to minimize the impact of it is to work on small iterations (agile) and be close to the client. One of the weakness in agile methodologies today is that the client representation (Product owner) is not aware of the client needs or too far from the client point of view.