Form still showing for one user

Hello,
I have an MDI application. Upon starting it, the MDI form is instantiated, then it kicks off a Username/Password log-in form and makes itself invisible(user never sees the MDI form). If the user logs in, the log-in form becomes invisible and the MDI form becomes visible. This works fine, except for one user. When the log-in form comes up, the MDI form is also visible. If he clicks on something, it crashes(certain variables aren't set at that point). If he logs in, however, the log-in goes invisble and everything works fine. This guy is a network admin/IS type and has several versions/hotfixes of the .Net Framework installed. Could that be the problem? Does anyone know what could be causing this problem for this one user and no one else?
Thanks

I'm not very familiar with MDI forms and applications but however, aren't you able to set the login form as startup form?
Double click 'My Project' from the solution explorer and on the tab 'Application' you should be able to set startup form

That's not really feasible at this point. The decision to make it behave this way was made a long time ago, before I ever started on the project. However, I believe there is a reason for doing it that way. One thing I can say is that you can close the MDI form and it brings up the log-in form again. That may have been why, but I think the person who did that isn't even on the project anymore.

Either way, I don't think that would fix the problem as there have been other problems like this("ghost" forms) elsewhere with this user(just this one user).