Just encountered a strange problem and I hope that someone can explain. I tried to create a mod to undo some of the changes in Weapon Mod Kit. I don't want the addition of a silencer to decrease attack damage. So I tried creating my own mod using Fallout.esm and WeaponModKits.esp as masters -- thinking that I would leave the published mod unchanged and simply load my mod after to revert the damage values. I changed damage values with no apparent problem. But when I re-load my mod in GECK to continue editing I get an error message that duplicate editor IDs have been created. And when the GECK opens up I see all the changes I've made showing up as duplicate IDs, and the original ones are there with the original (unchanged) damage values. If I make the changes using WeaponModKits as the active file then everything is ok -- no duplicates are created.

So I guess I can't use another mod as a master, but why is that?