Case where clojure.spec/unform returns invalid result according to spec

conform_unform_error.clj

(require '[clojure.core.specs])
(require '[clojure.spec :as s])

(s/def ::defn-macro (s/cat :type #{'defn} :definition :clojure.core.specs/defn-args))

(let [form '(defn foo "bar" ([a & b] a a c) ([a b] a))]

  (-> form
      (->> (s/conform ::defn-macro))) ;;=> {:type defn, :definition {:name foo, :docstring "bar", :bs [:arity-n {:bodies [{:args {:args [[:sym a]], :varargs {:amp &, :form [:sym b]}}, :body [a a c]} {:args {:args [[:sym a] [:sym b]]}, :body [a]}]}]}}

  ;; Unforming returns the function definition, but with the args in a list instead of a vector:
  (->> form
       (s/conform ::defn-macro)
       (s/unform ::defn-macro))  ;;=> (defn foo "bar" ((a (& b)) a a c) ((a b) a))) 

  ;; Conforming after unforming doesn't work anymore
  (->> form
       (s/conform ::defn-macro)
       (s/unform ::defn-macro)
       (s/conform ::defn-macro)) ;;=> :clojure.spec/invalid

    )