The provided project was not runnable due to a lot of missing references and files, but I saw the cause of the problem. It is caused by the fact that the Window inside the editor template is initialized inside a hidden container. As a result, its content wrapper receives a visibility:hidden style that you need to remove manually:
We came across this issue recently and will resolve it in future Kendo UI builds.
Join us on our journey to create the world's most complete HTML 5 UI Framework - download Kendo UI