Thanks Bogdan.

The YCbCrPositioning tag is considered "unsafe" to copy because it may affect the way the image is rendered. These "unsafe" tags are listed in the tag name documentation, and must be specified explicitly if you want them copied.

YCbCrPositioning is unique in that as well as being "unsafe", it is also a required tag according to the EXIF specification. Currently ExifTool sets this to "Centered" by default if not specified. This is why you get a different value for this tag.

Perhaps in a future release I will come up with a better way to handle this.

- Phil