Well now it is all starting to make sense. Pentax changed the hood for this lens mid-course. The slide on hood is simply a friction fit, although I believe there may be some sort of indent on the inner side of the hood collar that helps keep it in place but I'm not sure.
Troll's more recent manual shows the availability of a 67mm screw-in hood. Given the choice I would probably favor that one.
Perhaps this is why the Pentax Forum was confused.