The MainFrame is showing and the user click the logout button to call login function. The the CLoginForm show, CLoginForm is a no border CDialog, when user click the minimize button of CLoginForm. The CLoginForm is hide, but there is a black block in the left-bottom of the screem. I donot know why this happen.
My guess is that login being a modal dialog will prevent the parent window from processing things (like paint messages) until the modal dialog is dismissed. Might you use a modeless dialog in this case?