Glenn, it seems more likely that the pits produce some tar when first heated and this is causing the crusty, sticky, buildup. I ran a few hundred pounds of pellets through my combustioneer for the hell of it, just to see how they would burn, and when I stopped and switched back to coal, the coal didn't burn quite right. I cleaned out the pot and found what you're describing - which had never happened with my coal oiled with waste oil or mineral oil from TSC (I do a thorough cleaning of the pot and tueyeres bi-annually, and, after years of burning oiled coal never had that happen until I burned pellets). This leads me to believe that the pits have some potential to produce a bit of tar or creosote just like pellets (perhaps not as badly) at the point where they begin to get hot, but before they fully ignite in the burnpot.
Also, why don't the anthracite stokers have what ALL bituminous stokers have, which is a small tube from the combustion air blower (about 1/2" dia.) going to the auger tube? This tiny air tube leads back to the middle of the auger tube to put just a slight amount of pressure in the tube thus keeping all fumes and coal gasses from backing up into the bin. This system works very well and prevents any backflow of gasses not just into the bin, but prevents heat from the fire backing into the auger.