ESM REST API results for aggregated base events always have count of 0
I'm using the ArcSight ESM's REST API (https://esm:8443/www/manager-service/rest/SecurityEventService/getSecurityEvents) to collect event information with an external script. ESM v6.9.1.
The WSDL file describing the securityEvent schema shows 3 fields that appear to hold 'count' information: aggregatedEventCount, baseEventCount, and correlatedEventCount. I'm retrieving base events, so looks like aggregatedEventCount is the important one.
For base events that have type "BASE", aggregatedEventCount is always 1, as expected.
For base events that have type "AGGREGATED", aggregatedEventCount is always 0. This is clearly incorrect. The same issue occurs on multiple ESMs that were set up independently, so I don't think it's an issue with the settings of the manager.
From within the Console, I can clearly see that the events DO have an aggregated count greater than 0.
Has anyone else encountered this issue? Any thoughts of how to get the real aggregated event count through the API?