Depends on the feed rate, coal size and how much air passes thru the coals, our Keystoker/DV 90K does the same thing. Ours Varies quite a bit, from glowing orange to hitting the top too. Just depends on how it stacks up in the fire grate. The rice coal can vary in size and as it packs along the fire grate, less air can get thru, bigger sizes will let more air thru and burn differently. I run a small mix of Buckwheat (30%)/Rice (70%) or so, I just thow some handfulls of buckwheat to help elminate the clinkers/cakes from forming.
Nothing to worry about. The dampness of the coal shouldn't affect it, it will burn it off quite quickly as it's feeding.