-M option fails and reports success...
When invoking exiv2 with multiple -M options, the first is processed, and an error is given for the second, but the return code is 0.
$ exiv2 mo -M 'set Exif.Image.Copyright Ascii Me' -M 'set Exif.Image.Orientation Short left, top' _MG_3095.jpg
Warning: Exif.Image.Orientation: Failed to read Short value "left, top"
$ echo $?
This has high impact, since the second EXIF tag update has been reported to succeed, but didn't.