In admin panel > Edit Category > Category Layout > If you set to - Photo Gallery ...
... you will only have pics from that category, but it won't be default Group by Member per cat. Group by Member can be selected in the sort dropdown per category.
The problem that you pointed out with Group By Member - last uploaded photo thumb is not from the cat uploaded to - is a stickler for me too and the main reason I don't select the default cat view as Group by Member - very confusing to the viewer.
Hopefully bright minds at PhotoPost will be able to find a solution.
