If any given variable the xtrabackup-v2 sst script looks for is specified
  multiple times in cnf file then it tend to pick both of them causing
  some of the follow-up command to fail.

  Avoid this programatic mistake by honoring only the last variable assigned
  setting as done by mysqld too.

  Check https://bugs.launchpad.net/percona-xtradb-cluster/+bug/1362830