The current swank-allegro has a number of functions in it that are also defined in swank-backend. E.g.

;;; swank-backend

(definterface call-with-syntax-hooks (fn) "Call FN with hooks to handle special syntax." (funcall fn))

;;; swank-allegro

(defimplementation call-with-syntax-hooks (fn) (funcall fn))

My guess is that this is just an accident of history. If I don't hear otherwise, I'll clean up the allegro bit and check it in in the next few days.