Hi Alex,
I cannot answer your question, but I see the same in my programs. If I add programs = smart campaigns to the Engagement Program, neither engagement (always 90) nor unsubscribes (always 0%) are calculated correctly. Only in my very first Engagement Program, where I had added emails (instead of programs) to the streams, both engagement and unsubscrbes look somewhat real.
I haven't had time to follow this up with support, but IMHO there are still some bugs here.