P: Won't save updated GPS direction to the file

If you change an existing GPS image direction and do Metadata > Save To File, the new direction doesn't get saved.  (LR CC 2015.10.1 / OS X 10.12.5)

To reproduce:

1. Select a photo that has GPS coordinates but no GPS image direction:


2. Do Metadata Save To File and use ExifTool to verify that EXIF:GPSImgDirection is not present:



2. Change the direction to East:


3. Do Metadata > Save To File and verify that East was written to the file:



4. Change the direction to South:


5. Do Metadata > Save To File and discover that East is still in the file, not South: