When the preference "Other Options - Show current Plastic SCM user in the window title" is active, it always displays the username configured under "Preferences - General". If there are connection profiles stored under "Preferences - Profiles", this may not be the same user that is logged in at the active workspace. It may not even be a valid user at all, since you will be transparently connected if there is a valid profile.

To be really useful and accurate, the username displayed in the window title should be updated every time the active workspace changes - instead of blindly displaying the username stored in "Preferences - General" it should displayed the user that is actually connected to the server for the currently active workspace (the active workspace tab).