Feature Request Summary: 

Agents who are not the original creator of a side conversation, will be added as cc when a secondary agent replies to the same side conversation.

Description/Use Cases: 

Agent 1 creates a side conversation with an end user and leaves the ticket
When agent 2 enters the same ticket and wants to add or reply to the side conversation, agent 1 is automatically added as a receiver of the update to the side conversation.
This seems like weird behavior, as I would expect only the intended receiver to receive my new answer to the side conversation.

This behavior has been confirmed as intended by Zendesk Support.

My suggestion would be to create a setting where it is chosen if the original creator of the side conversation will be added in CC in future updates, or not.

Business impact of limitation or missing feature:

In our organization agents are not responsible for tickets from creation to solved, and therefor are spammed by side conversations they have no interest in, only on the basis that they created the side conversation.

They can manually be removed by the updater of the side conversation, but this is often forgotten and is also just a new click added to the workflow.