Server name added to Usernames after upgrade

After the recent platform upgrade to ver.10 most of the users has had the application server name added to the front of their username, ie: OSxxxxxxYYYxxxxxx/username.

This makes the username long and awkward to remember. 

While I can change all of these user accounts back to just username, I was wondering if anyone else has experienced this before and what actually causes it?

I'm hoping to prevent it from happening again if possible.

Hi Hoang,

That sounds strange. Where do you see this <server>/<username>? On the Users table itself or somewhere else? In all environments?

Haven't you changed anything on the authentication?