It's an interesting thing to research. I have heard lineage holders (not Karma Kagyu holders though) gloss this by saying different lineages hold different views on Father, Mother and Non-Dual tantra with Kalachakra and Hevajra being the prime examples of contention (esp. Hevajra). And it basically breaks down to whether the practice is more on the method side or the wisdom side.

Here is a point to "bake one's noodle" (excuse the plagiarized quote please).

The Gampo Abbey account says that "Lokeshvara Mahakarunikaya Jinasagara Avalokitesvara" ( Tib: Jigtenwangchuk Tug je chenpo Gyalwa Gyatso Chenrezi) - to refer to Him with the full name used in the Mandala Ritual Sadhana and the Great Commentary by the first Karma Chagme; is said to be father Tantra.

Thrangu Rinpoche is adamant on this on the basis that the "tradition" is father Tantra.

What is strange and noodle baking though is that in the commentary, the practices are referred to as the "essence of mother tantra" by Karma Chagme who wrote the main commentary used to this day.Jamgon Kongtrul also lists the Tantra as mother Tantra (please see the back matter in the Gem of many colours). The Drubthab kundu lists it among mother Tantras.

I have discussed this in depth with the late Bokar Rinpoche who looked it up in his personal note books and also verified that when he received the lineage, it was stated to be mother tantra.

Now to add further fuel to this pointless fire, Beru Khyentse Rinpoche and Khenpo Karthar Rinpoche have said that Jinasagara is non-dual tantra like Kalachakra.Bokar Rinpoche did say that over time as various oral instructions evolved the practice could have become defacto non-dual tantra. Thrangu Rinpoche did not want to refute this view and agreed in theory but otherwise, as is evident in the Gampo abbey site, sticks to his view that Jinasagara is a father Tantra.

Personally I have wondered about this for years and i would be appreciative of any ideas expressed by my learned Vajra sisters and brothers on Dharma Wheel.

However, for myself, it doesn't affect the practice itself and I am starting to see Je Tsong Khapas view that father mother tantras is an artificial demarcation that is essentially superfluous and that all Tantras are essentially "non dual" and can be practiced with one or another emphasis.

BTW someone mentioned a standing yab-yum Jinasagara - if one looks at those pictures carefully, you will find they are entitled "Guhyasadhana Jinasagara".

All the best to everyone and may we all be enveloped by the four limitless meditations.