The Full and incremental backup reset the archive bit of the files that are backed up. Therefore, if backup job fails, archive bit of files which have been backed up will be reset. However, other applications may modify the archive bit of the files. Refer to the following TechNote:
http://seer.support.veritas.com/docs/190786.htm
Also refer the following technote as well.
Title:- When running a differential or incremental backup by modified time, the backup will be as large as the full backup by modified time if the same selection list is not used.
http://seer.support.veritas.com/docs/258604.htm
We hope this helps.