When I add a user Alias because it's not recognized by default:
Guillaume Demers <IP-0A70D9BD\gdemers>
When I click Add the Alias is added as:
Guillaume Demers <IP-0A70D9BD/gdemers>
Notice the backslash changed to a forward-slash, therefore the user is never recognized.
This is a real problem if we want to switch form TFS to your system.