More weirdness with the buffalo horn.
Sawed just a couple of square inches of the stuff on the bandsaw. Then sawed some timber. Opened the bandsaw's lower door it was full of sawdust - clearly the dust extract wasn't working any more.
Some cleaning and I found the problem - a "dust buffalo" of white fibrous swarf, big and tough enough to block a 4" dust collector hose!
It's the weirdest stuff - it's like the stuff that comes out of chainsaw boots if you accidentally cut into them - deliberately fibrous and capable of blocking a saw.