MIE format supports information in other native formats, so using -all:all is significant, and will keep the information in its original location (format). Without this, information will be preferentially written to EXIF, IPTC and XMP in that order. This is true for many other file types as well, since there are other file types that also support these types of information.

By this logic, copying from XMP:DateTimeOriginal without specifying a group will write by EXIF:DateTimeOriginal and you will get a timezone specifier in your EXIF date/time string.

The tags are copied in the order they are encountered, so if a file contains both EXIF and XMP information and both contain a tag with the same name, then it is the second tag that is written.

About removing or not removing the timezone when writing to EXIF: The current behaviour is clearly inconsistent, so unless anyone objects I will make a change in exiftool 7.15 to use the following logic:

1) If no timezone exists when writing an XMP date/time value, the local timezone will be added unless the -n option is used.

2) If a timezone exists when writing EXIF information, it will be stripped off unless the -n option is used.

- Phil