I getting puffs of smoke out of the stove?

Stan! Your still around, wondering when you would grace us with your presence. Guessing the new cats have been working well for you since I hadn't seen much from you lately.

Your chimney setup has always been a bit of concern and I think this is just a reflection of your setup.

I used to get that happening when my Jotul was turned way down. No matter what, it would occasionally puff back because all of a sudden, some of the wood would ignite the gases. You could actually see the thing ignite if you looked in the box. It would puff right out of the top of the stove. I think this only happens in cat stoves, but I could be wrong. I rigged up a washer that I installed in the rod that closes my stoves draft. The washer prevented the draft from being fully closed all the way. It seemed to allow just a little more of the gases to escape. I tried everything else and nothing would work. I know in a fire turned down all the way, no matter what, it would puff back. I had dry wood, a hot fire going which I slowly turned down, and a chiminey with good draft, that was high enough. I tried everything. Just my advice!

Sounds to me that your flue is just getting to cool. I had the same situation with my old stove if the temp dropped below 300* it would back draft every time.