My Alaska has a separate combustion fan that runs 24/7 on full speed, I can slow the burn w-a-y down without any problems. The fire should never move back past the air holes in the grate. If there is burning going on farther up the grate then there has to be air getting in through other unsealed areas.
I would shut the stoker down and check it out. One weekend before the end of the month I'm shutting down the Alaska for maintenance, I'm going to check the sealant around the grate as well. Since January it has been burning non-stop except for a few power outages when I wasn't here to power up the generator, out for a day once when I ran low on coal, and out when I did the stoker fan conversion.
I had a similar issue the other night with my Console II
Is this a paddle feed or a carpet like mine?