First off, don't meld gear that isn't capstone gear. In fact, don't meld gear below level 100.

Second of all, in this game gear progression involves picking the gear with the best substats (that is crit, determination and direct hit, order depends on your job) and then melding whatever is missing. So unless you're melding a healer, you shouldn't have this problem, and if you do, you should retry melding at lv100.