When saving a movie, the highest resolution is 1920x1080.  Even when you set a custom resolution, it will not let you choose a number greater than 1920x1080. 

If the custom resolution did not have this limit, then I could save videos to my native screen resolution (3840x2160).  The clips that I put together are in 4K, but when you save the movie, it can't save in 4K.

:(

Does anyone else want the custom resolution to allow higher resolutions?