涉及TopMost和Invoke的Z-Order问题

I am showing Dialogs with Form.ShowDialog(). Forms are set to TopMost. Some image processing calculations are performed asynchronly in the background. Their results are rendered in the main form by Invoke. So far so good. Strange thing is that every now and then the modal dialog is moved behind the main form. I guess that happens when the messages that build up the dialog are somehow "disturbed" by Invoke. I am showing Dialogs with Form.ShowDialog(). Fo