POA table cascading relationship on phonecall create

Hi,

I am trying to identify which relationship is causing POA table growth in Dynamics CRM 2013, and have some pointers, but want to get more information before I move ahead.

We have a phone call routing system that calls the CRM web service and creates a phone call activity when an agents desk phone is ringing. I don't have too much control over this call to the WS, it is a third party finished product integrated with CRM. The system has a service account which has CRM access, but sets the call agent (recipient) as the owner of the activity. In the POA table I can see millions of rows with:

• PrincipalID = the service user ID (f.ex. ID belonging to 'domain\x_ivr')
• ObjectID = the phone call activity ID
• ObjectTypeCode = 4200 (note that this is activity, not phone call directly, could be relevant)
• PrincipalTypeCode = 8
• AccessRightsMask = 0
• InheritedAccessRightsMask = 135069719

From what I can tell, this means that when the record is created, it is automatically shared with the service user. However, the relationship between systemuser as owner and phone call activity is not editable (type = system). The global setting "Share reassigned record with owner" is set to "No".

Any hints on what might cause this behavior or where to look?