Case Activity Export with custom fields creates multiple rows for a activity

When exporting case activities with custom fields (from Find Cases => Export => Select Fields to Export), the export creates multiple rows of the same activity type.

Replication Steps are:

1. create case type
2. add 2 or 3 activity types
3. add custom field to one of the activity types
4. create new case
5. export out fields - case id, activity date/time, activity type, custom field that added above
6. should get 1 row for each activity, instead got 9 rows exported
7. then add data to case activity, add data to the custom field and repeat above steps
8. this adds two more rows to the export

See attached, its a comparison between export with no custom field columns and export with custom field columns (but have not filed in the custom fields)- export with custom field columns is repeated 9 times.
and
Once the custom fields are filled in and exported, compare between export with no custom fields filled in and export with custom fields filled in - after custom fields are added 2 new rows are added