yeah, I've run into the same problem as he did:
basically, the seam nodes gathered from the chunk's neighbors
generate polygons which coincide with the neighbor's polygons.
i.e. octree nodes collected from a neighboring chunk generate polys between themselves.
when later the neighbor's mesh is built, it will also generate the polys in the same positions.
maybe, there's a better algorithm for generating seams?
because all 7 neighbors (connected to the chunk via a seam) must be re-meshed whenever the chunk's LoD changes.