What is that ?

I was exploring Skill_Projectile in the stat editor, then I was going to copy one of the skills but I chose "Create derived in (my project)", thinking it would create a new entry in my project, but instead it created a new Projectile entry and deleted all my custom projectile skills. I did not save and I closed the editor without saving but still the modification got saved somehow and I lost all my projectile skills ? Wtf is that ?