Channel Framework - channelback respoonses are being sent as email

Hi,

We recently integrated two custom channels using the channel framework.

When a ticket is created, if the end-user account is also populated with an email address, we see 3 comment options. These are comment via;  1-channelframework, 2-email only, 3-private note. The default option is comment via channel framework to channelback agent response.

The problem is when we add comment via channelframework, the response is being sent both on the customer channel and as an email. Zendesk support says this is expected behaviour. The comment is public, and if there is an email notification trigger and the customer has email address field populated the comment will be sent both on channel framework connection and as email. This doesn't make sense to us. Does anyone have experience with this topic?