innobackupex fails with 'no space on device' but completes with OK message

Ran innobackupex with the command below. Device really did run out of space during rsync, but still completed with status of OK. This is not supposed to happen it should not end with OK message if something went wrong. My automation depends on not finding OK as indicated in the manual. It indicates it will only print OK if it really worked.

This seems like a bug, am I missing something here?

Command line: innobackupex --defaults-extra-file=/etc/mysql.cnf --backup --compress --parallel=4 --rsync --incremental --incremental-basedir=./full_backup_20151216/2015-12-27_01-10-11 ./full_backup_20151216

Log…

[B]
[B]

151228 01:10:11 >> log scanned up to (14900595284937)
.
. lots more log here removed for brevity…
.

Should I just post this as a bug? Not sure how exactly to submit a bug for xtrabackup. It clearly should not complete with an OK message when the backup is not complete.