I wonder at this problem. If Cross Mount Points is not checked, files under /mnt mount point are not backed up although file list contains root file system.
What entries are written in your file list?
Workaround is adding /mnt in exclude list. For detail, see Administrator's Guide for UNIX, page 139.
VERITAS NetBackup 5.1 System Administrators Guide for UNIX, Volume I
http://support.veritas.com/docs/268090