This might allready be a known fact and it is certainly not going to help a lot if it isn't but the reason why some civs that are forbidden to negotiate still negotiate is this:
The "talker" is really not the one starting the negotiation, if for example the polish sneak attack Brandenburg (in a scenario which might take place around 1600) and brandenburg is allied to sweden, brandenburg will contact sweden and ask for help, in this situation the polish are the talker, since it is thier turn. Thus no negotiation events between the brandenburg civ and the swedish civ will trigger, they could still end up whit a broken alliance that is going to be very hard to recreate for the player (since he can't contact the other civ).
If the human player moves a unit next to another civs unit the other civ will sometimes ask for an audience, in this case the human civ is the talker since it is thier turn and so on.
Altough this is enlightening it wont be of much help I guess, and it might be a known fact allready in which case this post was a complete waste of time, oh well
