RDP: why does the username alternate between domain\name and name@domain?

RDP: why does the username alternate between domain\name and name@domain?

I tend to RDP around a number of different machines both at my office and remotely at various customers. Each time I connect to a destination, Windows presents me with a login dialog that remembers who I logged in as last time (without the password because I don't like having the system remember any passwords).