I'm open to suggestions, but currently exiftool does not strip the timezone from the date/time string when an XMP date/time is copied to an EXIF date/time. I know this goes against the EXIF specification, but to be truthful the EXIF specification should have included the timezone information in the first place.

So this will happen if you copy the XMP:ModifyDate to EXIF:ModifyDate. If this is not what you want, you can copy the tags to the same groups by adding -all:all after -TagsFromFile. (Note that if you do this you should also add -xmp:all if you want all XMP date/times to be copied due to a bug which has just been discovered, but this will be fixed in exiftool 7.15).

- Phil