Dear friends,
I had the same problem with VDPA 5.5.5.180 and I am still having it after the upgrade to 5.5.6.56.
After a successful backup of a VM, the snapshot created for the backup job is not committed.
I can see on the Recent Tasks in VSphere Web Client that VDP is trying and successfully commits the snapshot, but unfortunately the next backup fails due to the remaining snapshot.
The snapshot does not appear in the Snapshot Manager and the 'vim-cmd vmsvc/snapshot.removeall' does not finds any snapshot to delete.
I have to follow KB1026380 in order to create a new snapshot (vim-cmd vmsvc/snapshot.create xxx my_snapshot snapshot_test 0 0) and then run the 'snapshot.removeall' command.
After that, the directory is clean from snapshots, and the backup job runs successfully. But only once 
Any help or ideas will be appreciated.
Petros