Backup type "datafile incr"

Databases are Oracle version 11.2.0.3. We run our backups using Netbackup which calls a script that calls BRBACKUP which calls RMAN. Backups are all to a tape library.

I was looking at the output of the following query on our systems.

select end_time, to_char(output_bytes/(1024),'999999999999999.99') "Backup Size (KB)",input_type

from v$rman_backup_job_details order by 1 asc;

On most databases all of our backups show as input_type "DB INCR" but on a couple of them the level 0 incremental (full backup in BRTOOLS) shows up in this listing as a "DATAFILE INCR". The other backups on this same system show up as "DB INCR". I'm wondering why this is different on some systems. Is there a difference between the two types? I don't find any references to the "DATAFILE INCR" backup type on the web, on Oracle support, or on service.sap.com.