Both times the name was taken from me by a Facebook employee and eventually given to this Mat Henley guy from Uber.
Screenshots of Facebook staff forcefully resetting the account names:
https://i.succ.in/WuwuV1IH.png https://i.succ.in/WuMMtKTr.png (The revert button does nothing, just offers to change your password)
It seems like FB employees do not need a particularly good reason to go play around with admin tools editing user accounts. If they can edit users accounts this lightly, what does it take for them to look through you private posts or messages?