Unsubscribe from a group mailing list unsubscribes also from all child groups

I usually use a parent group to manage the newsletter mailing list. People can join directly to this group through the corresponding subscribe profile but at the same time we nest to this main mailing list a set of smart groups of contacts that by default we want them to receive newsletter (e.g. Volunteers, Donors, Staff, etc.). It works nice for our purposes.

Recently but, I have noticed that we have a problem with the unsubscribe form linked to mailings.

The unsubscribe form show parent group and all their childs when in the end we only expect the parent group to be shown. If the contact continues with the unsubscribe process it is automatically removed from all groups.

It is the expected behavior? Does anyone else use this method and find that problem?