WEB-2258Invalid character names
This bug has been private for around a year, and has finally been leaked. I just learned about it today.
Basically, it's the result of a Unicode case mapping collision. This site can explain it better than I ever could: https://eng.getwisdom.io/hacking-github-with-unicode-dotless-i/
Some examples of these can be seen below: (note that is a Cyrillic K)
https://namemc.com/profile/Kha.1
https://namemc.com/profile/Evİlnayo.1
In the comments is a cURL formatted example of a post request used to do this. As far as I know, it can not be done through my.minecraft.net, only the Mojang API.
Note from [Mod] Urielsalis: Some servers have trouble targetting this users for commands, like /kick or /ban
