Not just themselves, often it's stolen to order: there's been a few mainstream stories about this and they often mention that paying off Facebook employees is pretty commonplace because the value of these usernames and the low paid customer service representatives are a recipe for bribery.
Just my personal observation. I earned around half a million dollars by running an "autoclaimer" that would automatically register Instagram names as they'd become available. I'd regularly see Instagram employees grabbing names from my portfolio for themselves.
If you could post before / after screenshots showing proof of this theft somewhere - along with the real-world names of these employees -- that might get a lot of eyeballs.
wait what? how are they not fired, thats got to be against the "community guidelines" (unless of course its for an advertiser or political organisation. )
I assume they aren't emailing Mark Zuckerberg with every account they steal. All it takes is lax internal auditing and a culture where customer service[1] is not valued and this could go on for a very long time.
[1] Ok, this is a little unfair. They do have customer service, but what they don't have is product service, and this guy is just part of the product, not a customer.
This happens all the time, there is no recourse. Instagram employees are constantly taking usernames for themselves.