Mastery 7 Emote Bug

You see it all the time. A player dies, and then their dead body displays their mastery emote.

But, since I have gotten to level 7 mastery with Zyra, I can no longer do this!

My mastery 6 still works on other champs, but the only champ that I have level 7 with, Zyra, no longer works. I can't flex my emote after I die!!!

Thus, I can not verify that this is for all champions. I have asked on the League subreddit but it gets buried every time.