Found this: Seems to be related to wood and burning technique
http://www.chimneys.com/burning_secrets/chapter_5.html
Backpuffing:
Backpuffing is essentially small explosions in the stove, forcing puffs of smoke into the room through every available gap in the stove or stovepipe. It is caused by a combination of reduced airflow into the stove and use of too-dry wood or wood that's split so small that it burns too rapidly. Instead of the gasses burning as they are emitted, they collect in the firebox. Oxygen slowly enters the firebox, and when there is finally enough, the gasses ignite.
The problem of backpuffing is also a good reason not to burn things like kiln- dried wood blocks, pallets, and trimmings from woodshops, except as kindling.
Tip #3: Learn the right way to build a fire. If you are not a seasoned firebuilder, see How to Build a Fire, page 15. In a woodstove, the trick is to use enough kindling and small splits of wood to establish a bed of coals quickly, then to add larger logs.
Tip #4: Avoid long, low fires. Especially if you have an "air-tight" stove, avoid low, smoky fires. Yes, long burn time is a convenience. But believe it or not, you are getting much less heat from your wood if the fire is smoky.
Jets of smoke emitted from a wood stove, caused by the ignition of a buildup of combustible gasses in the firebox.
In short, backpuffing is caused by an inadequate flow of oxygen into the firebox. Instead of burning steadily, combustible gasses build up in the firebox and periodically ignite in a small explosion, forcing smoke out of the stove through every available opening, including the air intakes.
What might cause your stove to backpuff?
Generally, shutting the air controls down too far, starving the fire of oxygen, AND:
either Using super-dry wood, like pallets or kiln-dried wood blocks, which burn very rapidly, emitting too much combustible gas too quickly. (See page 53 for details.)
or Using firewood that is split very small, which also burns too rapidly, creating an excess of combustible gas in the firebox.
Backpuffing is fairly easy to diagnose: Try opening the air control on the stove. If the smoking stops, it is very likely a backpuffing problem. Of course, you shouldn't over-fire the stove, either. If you have to open the air control to the point that the stove will overheat before the backpuffing stops, then reconsider your firewood supply. Either get a new load of properly-seasoned wood, or try mixing less- dry or larger pieces with the super-dry or small-cut pieces. (See page 52 for details on firewood selection.)