I know the cause of the menu problem, but not the solution.
The menus display incorrectly when the D application is run on Windows. Apparently, menus display properly when the application is compiled and run on a Linux system (I used CentOS 7 to test the application). On Windows, however, the same code displays the menu at the top left corner of the screen (position 0, 0).
This is definitely a bug that manifests in the Windows version of the library. I am uncertain whether it is in GtkD or in the Gtk runtime itself.
This bug needs to be reported, but I cannot find a place to create a ticket. Can someone tell me if there is a place to report this bug, and if so where that place is?