You can disable snapshot handling or enable CBT.
For CBT disabled backups, snapshots will remain in the datastore after backup. (Max upto 2, For INCR/DIFF)
If CBT is enabled, there will be no snapshots in datastore after backup.
Occassionaly snapshot may remain, if any network outage/ datastore fluctations, so that DP is not able to contact VCenter. So make sure your datastore is not fluctating.