Agree with Diane, freezing in sugar syrup is supposed to help preserve the quality.
http://nchfp.uga.edu/how/freeze/melon.html
Seems to me that whenever I tried to freeze melon balls/pieces, it did just what you experienced. Will look a bit more into it. Peach slices can be frozen with good results. I'd use lemon juice or fruit fresh to keep from browning and freeze in a single layer on a cookie sheet. Pack into freezer bags or vacuum seal (the best choice) and freeze.