Have you ever commented in the Cafe section? If you comment in both like a lot of people do then for me I like to go back and read the new posts in those threads which is what causes the toggling. I am not sure I see the difference between the Cafe and the Parent. If someone posts something at the root of forum, would you be able to accurately guess where to move that to?
Ideally, one should be able to choose between a subgrouping view and a list view