Differential Incremental backup running as FULL

Hi

Here is my setup: 

OS: RHEL5

File system backup: Cold backup RMAN files

Issue: Differential Incremental backups scheduled during weekdays runs as FULL backup on the FS

Schedule Types: D-D(Differential Incremental backup) - Frequency based- Runs every day (except Saturdays) 

W-F (Differential Incremental backup) - Calendar based- runs every Saturday (Excluded on last Saturday of the month)

M-F (FULL backup) - Calender based-runs on every last Saturday

Here we use Ctrl M as schedule and dependent on RMAN jobs, we have one FS that is /orabkup and in this FS we have data_l0 (level 0-FULL) and data_l1(level 1-Incremental)

Every day RMAN INCR job removes the old files and dumps the changes ones in level 1 folder. On Saturday (W-F & M-F) RMAN FULL runs and removes old files in level 0 and dumps new files which will be a FULL backup.

Once the Saturdays W-F gets completed and the D-D the next day NBU takes the backup of both level0 and level1 directories under the /orabkup FS even though the modified time is only the time stamp of the weekend.

This is causing the issues with all the backups overrun.

I suspect the problem is with Frequency based D-D backups as the W-F/M-F will run until next day say 15:00 hrs Sunday and on Sunday when INCR D-D backup is initiated the backup is FULL with the same amount of data that is backed up as FULL.

The Frequency is set as 6 hours. 

Please guide me if I need to change the frequency based schedules.