I was scrolling through the standings of round 856 when I saw https://mirror.codeforces.com/profile/tyler participated in the round as a Master but it was still rated for him.

The only way I can think this is possible is that he signed up for both rounds well in advance which allowed him to sign up as a rated participant when he was still a CM and then after he made Master, he was still able to participate as a rated contestant.

Either way, pretty funny.