TSM NDMP no Differential, only FULL

We have an EMC Isilon configured with a Backup Accelerator and cannot perform differential backups using TSM 5.5.

There are several virtual filespaces defined on TSM, and run backups on a weekly basis.
Numerous FULL backups have been executed across all filespaces, even test filespaces with less that 10MB of data, all complete Successfully according to the TSM actlog.
However the backups always default to FULL even though mode=diff is defined.

The command we use is -
backup node isilon /backupfolder toc=yes wait=yes mode=differential

This occurs on every filespace. I can scroll through the TOC for each filespace, and can restore the entire filespace to an alternate location without problem, so the backups are definitely working, however no differentials work.

Any ideas?
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PearsonAusAuthor Commented:
anyone have any ideas as to why this could be happening?
Screendump of act log

tsm: TSM01>backup node isilon /BackupTest mode=diff toc=yes wait=yes
ANR0984I Process 215 for BACKUP NAS (FULL) started in the FOREGROUND at 10:52:23 AM.
ANR1063I Full backup of NAS node ISILON, file system /BackupTest, started as process 215 by administrator TEST.
ANR1067I NAS Backup process 215 completed.
ANR0986I Process 215 for BACKUP NAS (FULL) running in the FOREGROUND processed 1 items for a total of
11,993,088 bytes with a completion state of SUCCESS at 10:53:45 AM.

This has now been run around 5 times, same results. TOC is fine, and I can also perform a full restore on all data.
PearsonAusAuthor Commented:
anyone able to assist?

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PearsonAusAuthor Commented:
no response given. Solution found locally.
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