I had problems with the May 17, 2007 NYT puzzle which has some answers with multiple letters per square. This same thing occured in MacXWord as well. After inserting some multiple letters in one square, other letters in the nearby area change randomly on their own. I believe, but am not certan, that this only happens if I have used Solution > Reveal > Current Word before inserting the multiple letters. After this beings to happen, the puzzle cannot be worked.