If the entity is not the owner of the association the association is not percieved as being a member of the entity and therefore the GetChangedMembers will not detect the change as this looks at the members of the entity.
Removing the stakeholder from the report is therefore a change of the member of the stakeholder and will be shown with the GetCHangedMembers perfromed on the stakeholder entity.
So to get your complete information you will need to combine the values for the changes on both the report and the stakeholder entities, or store the deleted stakeholders temporarily in an association opwned by the report entity.