Conversation Threading: Quick Reply how edit recipients CC?

We're playing around with 18.1 and conversation threading.

When using quick reply you can enter recipients only in the "to:" field. There's no CC and BCC field. :confused:

Is there a solution to add recipients to CC or BCC.

Already tried typing cc: in front of the mail address, but it didn't work. ;)

Client 18.1.0 132896.