I purchased a Hawkmoon from Xûr months back and recently decided I'd finally get around to earning the catalyst given the buff to Hand Cannons. However, when I went to inspect the weapon, I noticed the Rangefinder perk I had on it was missing, and it was replaced with Transformative. From my understanding, Transformative was the original perk from the quest. However, I never did the quest. I purchased Hawkmoon straight from Xûr, yet the perk's been replaced. The only thing I did recently with the weapon was browse my collections to read about Hawkmoon (since it's unique and doesn't have set perks like the others), but I never attempted to claim it from there. Yet when I checked my Vault for the Hawkmoon I already had, it had Transformative.