Supplier contacts not mentioned in negotiation can respond to a negotiation?

Summary:

Hi Everyone,

I selected a supplier contact while creating a negotiation and didn't check 'Notify All Contacts' button. After negotiation is active I noticed that other supplier contacts could also see the negotiation in the Supplier Portal. Why is that happening? Shouldn't the supplier contact I have selected should only see the negotiation?

And if all contacts can see the negotiation always then what's the purpose of selecting a supplier contact during Negotiation creation?

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