Earlier versions of GNU tar understood -o command line
option as a synonym for --old-archive.
GNU tar starting from version 1.13.90 understands this option as
a synonym for --no-same-owner. This is compatible with
UNIX98 tar implementations.
However, to facilitate transition, -o option retains its
old semantics when it is used with one of archive-creation commands.
Users are encouraged to use --format=oldgnu instead.
It is especially important, since versions of GNU Automake
up to and including 1.8.4 invoke tar with this option to produce
distribution tarballs. See v7, for the detailed discussion
of this issue and its implications.
Future versions of GNU tar will understand -o only as a
synonym for --no-same-owner.