EVENT_CHATTER_BEGIN doesn't always fire

[Terrillyn]

I've noticed some dialogs in Eastmarch are not triggering the EVENT_CHATTER_BEGIN event,
is this a known bug or unknown that needs reporting or do some special dialogs that not trigger this?

specifically:
During the quest "Shrine of Corruption" knocking on the door of the "Keeper's Home" at the beginning of the quest doesn't trigger this event, even though it starts a dialog; there have been a few others too, I think a couple of NPCs in Windhelm do this too.