Duplicate Protection?

Hi there! I hope it is right to put this under “technical”. I opened my classic pack I got from brawl Monday, May 4, and got a non-golden version of a rare card I already had 2 golden ones of. Is this working as designed cause of golden/non-golden or a bug? I did at that point in time not have all of the rares of classic twice.
Thanks for the help!

If you have all cards of a certain rarity from a specific set, you’ll start getting duplicates.