Question about transitivity in MultiFn.prefers() --- possible bug

[John Alan McDonald]

prefers(x,y) checks the ancestors of x, and returns true if any of them are preferred to y --- which makes sense to me.

However, it also check the ancestors of y, and returns true if x is preferred to any of them, which I don't understand. 

Is that the intended behavior?  Seems like it should be checking the descendants of y.

What I am I missing?

[John Alan McDonald]

A related but slightly different issue: is prefer-method supposed to be transitive?

That is,  (prefer-method f a b) and  (prefer-method f b c) implies (prefer-method f a c)?

Here is a unit test that checks for transitivity (which fails in Clojure 1.8.0):

(test/deftest transitive

  (derive ::transitive-d ::transitive-a)

  (derive ::transitive-d ::transitive-c)

  (defmulti transitive identity)

  (defmethod transitive ::transitive-a [x] [::transitive-a x]) 

  (defmethod transitive ::transitive-c [x] [::transitive-c x]) 

  (prefer-method transitive ::transitive-a ::transitive-b)

  (prefer-method transitive ::transitive-b ::transitive-c)

  (test/is (= [::transitive-a ::transitive-d] 

              (transitive ::transitive-d))))