Subscribe to new forum topic

I have subscriptions *almost* working, but can't figure this one out.

I want users to, by default, receive notification of *ALL* activity in the forum--new topics AND comments. For some reason, they are not notified of new topics.

Under "User default" I turned on subscriptions to Forum topics (checked both "on update" and "on comment").
Under "Categories" I checked all options under "Forums."
I have manually added all these to existing users (since I don't see a bulk way to update all users).

Still, no luck. Am I missing a setting somewhere?