Phase development in the MULTAN procedure is based on the permutation of the starting phase set. When a new phase of a gereral reflection is derived from the combination of two special reflections of the starting set, it may result in large error. If this occurs in the early stage of the phase development, the error is difficult to be eliminated afterwards. The wrong phase should then strongly affect the process of the phase development and leads sometimes to the failure of the structure determination. One way of dealing with this problem is to check the convergence mapping carefully and change some of the reflections in the starting set. Tests have been made on modifying a starting set that led to the MULTAN failure. It turns out that just a slight but proper modification of the starting set can greatly improve the process of phase development and leads to the correct solution of the structure.