Suppose that you have an add-in, like my MZ-Tools add-in, that has a feature that needs to open (invisibly) each form of a project to (do some review, modify some properties of controls, etc.). In that case you need to call ProjectItem.Open(EnvDTE.Constants.vsext_vk_Designer) to get the EnvDTE.Window, which remains invisible (you would have to call Window.Visible = True), and then get the Window.Object property to cast it to IDesignerHost. If the operation is very long because the project has many forms, chances are that the user will want to minimize the Visual Studio IDE to do other things meantime. However, due to a bug introduced in VS 2005 (it didn’t happen in VS.NET 2003), the IDE is annoyingly restored from the minimized state each time that a form is processed.
Here you have the article that I have written with the details:
BUG: ProjectItem.Open(EnvDTE.Constants.vsext_vk_Designer) restores the IDE from minimized state
And the bug report sent to Microsoft if you want to vote to fix it or track its resolution (hopefully they fix it because it ruins the user experience):