Consider the following scenario. You have an application that has several owned WS_EX_APPWINDOW pop-up windows. Then, a user selects an inactive window in this application from the taskbar of a computer that is running Windows Server 2008 or Windows Vista. In this scenario, the currently active pop-up window is selected again.
For example, assume that an application has a main window and the owned pop-up windows C, D, and E. Pop-up window D is active. You click the button on the taskbar for pop-up window C or E to make that window active. Instead, pop-up window D remains the active window.