I think I have discovered a bug but I don’t have a proper reproduction, but I can easily show examples of the issue, and I think my theory might be right.
Here is the issue, you are able to add non existent emoji to the post reactions. it results in
:whateverYouWant: reactions in posts.
You can see example of it on the Manjaro forum, where I noticed a specific user posts often have these non existent emojis. After asking him a few questions I concluded he’s using some kind of automatic translation extension in his browser, and that probably translates the emojis :code: to his language. Unfortunately I didn’t have a reply from this user to know exactly his setup on his browser. To back my theory, you can see when he quoted someone in the following thread linked, he had translation of the original message in his quote.
See this message/thread on Manjaro forum:
See an example in the reactions, you see the issue clearly with all the proper reactions next to the invalid one:
So it seems that a user can send non existent emojis through the process of no verification of the emoji code.