Incremental vmware backups do not work when using CASO and MMS

Having this problem since installing BE 2014 on vmware 5.1 U2 on Windows 2012 virtual servers running to Quantum DXI 4601 dedupe storage.

Full and incremental Backups of vmware work fine if run alone on CASO or media servers only,  but when the media servers are in a pool used by the CASO to delegate the job the incremental jobs always do a full backup saying they cannot detemine the backup status and hence do a full backup.

The CBT is obviously working but something is happenning on the delegation.

Engaged with Symantec backline tech support for just over 5 weeks now and they have no ida what the problem can be?

Thanks Howard