Activity based Views that use Groups as Filters results in double joins

I set up an Activity based View to be filtered on a Group that the Target was in.

Outcome was the rows for the Target contact went from 1 per Activity to multiple rows (I thought it was showing as many rows as there were Groups that the contact was in).

Torrance says he confirmed that the _civicrm_group_contact_union table is being joined twice but that this issue exists without this module too: ie in a standard civi install, the civicrm_group_contact table is also being joined twice. These leads to a doubling of rows.