Hi Phil,
Maybe I've complicated by explaining my issue -trying to be specific :-)

I am interested on XMP section inside DNG. If I use exact this command:

exiftool -tagsfromfile test.DNG -all:all result.MIE
-then all XMP tags are saved into MIE file, except xmp:DateTimeOriginal and xmp:DateTimeDigitized. Of course, resulting MIE also contain plenty of other metadata, but I'm focusing on XMP in this case. How come above tags are missing inside MIE?

If I execute (for the same DNG file):

exiftool -tagsfromfile test.DNG -xmp:all result.MIE
-then both, xmp:DateTimeOriginal and xmp:DateTimeDigitized, are not missing inside resulting MIE file.

See, using "-xmp:all", copies all XMP data into MIE, but if I use "-all:all", two (DateTime) tags are missing (all other XMP tags are copied).
This doesn't happen if source file is JPG.
Btw. both, DNG and CR2 (which was source for DNG), aren't manipulated. I would send you a DNG, but don't have your mail address by hand...

Thank you for patience,
Bogdan