Have you ever done that with a bracket fungus, Doug? It's not a surface form of rot. The mycelia live within the wood secreting cellulase enzymes to "eat" it from the inside out. The fruiting bodies that can be seen in the pictures are essentially wood that has been dissolved and used to build a new structure by the fungus. With most of the wood actually being lost into the atmosphere in the form of carbon dioxide during the process, I wouldn't be surprised if the fruiting bodies are more solid than the wood underneath at this point.
