Damn you Observer
Damn. Found a Rails Bug – if an observer is created before a subclass (in this case, when UserActionObserver gets instantiated before my new CommentablePage object), then observations don’t apply to the subclass.
Now I have to decide between patching that in (and potentially getting disrupted when rails catches up) or just making sure that things load in the right order. Annoying. I think I’ll go for the former.