I believe an old paint stirring stick would be better than what you are putting in the smelt, or wood shavings, ie, sawdust. I ran out of lead flux one time and thinking just any old flux would work, went down to welding supply store and picked up a can of solder flux. Big mistake. Popped all over the place. don't know what's in there, but lead didn't like it.
Many use chunks of wood to clarify the smelt. I never liked the smoke, as my Buck Beaver flux is pretty much smokeless. A simple remedy would be to change flux, and/or flux more i fusing the correct flux.