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.