Task aggregation does not work with approval groups?

Summary

Task aggregation does not work with approval groups?

Content

We have the below requirement in AP Invoice approval workflow. 

There are 2 approval groups created in BPM for AP Invoice approval. 2 approval groups will be triggered sequentially via bpm rules and one person needs to approve in each approval group(Single type participant)

There are some users who are in both the groups. If an user approves the first notification, he should NOT get second notification again for approval(from 2nd approval group).

We tried with task aggregation option. But it is not working. User still gets 2 notifications - one from each approval group.