I actually had that happen with my CB E-2300 (Gasser, by the way) a few times my first year burning. Only happened after having the bypass damper open to add wood during a high demand time when there was a roaring fire going and I was just topping off the load. But a couple of times it stayed burning out the chimney even after the bypass damper was closed. Come to find out the bracket that holds my damper in position was too weak by design and wasn't holding the damper in the right place causing smoke to leak out and creosote to form around that area.
That is very similar to the way a gasser burns. It is a very impressive sight looking at the torch-like flame coming down into the combustion chamber of a gasser. It's not much differant than looking in through the sight hole of an oil-fired burner. I'm sure there are other videos out there, but there is a good video of the P&M Optimizer 250 on youtube. Worth checking out if you've never seen one.