If you give the sender email address to the CC field and on the project settings you chose the "sharing to other users in the same organization" option, you get an error which says, that you are not in the same organization with yourself.
It seems to be the intended Service Desk behaviour, so we need to handle it.
Wild guess for solution:
In the ServiceDeskAPIV4 in the createRequest method, we could check that we don't add the participant name to the list if it is the same as the reporter. Did not test it yet, but will do.