What you want from autocrypt may be a “strict” setting. (Different story.)
Deltachat only puts message textin the subject in cases when sending plain text messages, i.e. to a contact with which no established autocrypt connection exists. For example to contact someone not yet using deltachat.
But the same subject visualization can actually also serve to visualize the encryption state:
So I guess, no encrypted stuff is repeated in another channel.
You may check out that “memoryhole”, though. https://github.com/deltachat/deltachat-core/issues/70