Strange behaviour of merge and into with map where keys are instances of AsyncChannel from http-kit

gistfile1.clj

(ns clj-test-server.core
  (:use org.httpkit.server))

; https://github.com/http-kit/http-kit/blob/master/src/java/org/httpkit/server/AsyncChannel.java

(def clients (atom nil))

(defn handler [] 
  (future (let 
              [merged (merge {} @clients)]
               (println merged)) ; => #<ManyToManyChannel clojure.core.async.impl.channels.ManyToManyChannel@5d9c832a>, but expect to get copy of @clients
            #_(let 
                [into-map (into {} @clients)] ; here I get exception <IllegalArgumentException java.lang.IllegalArgumentException: No implementation of method: :take! of protocol: #'clojure.core.async.impl.protocols/ReadPort found for class: nil
                  (println into-map))))

(defn ws
  [req]
  (with-channel req con
    (swap! clients assoc con true)
    (println con " connected")
    (on-receive con (fn [data] 
        (handler)))
    (on-close con (fn [status]
                    (swap! clients dissoc con)
                    (println con " disconnected. status: " status)))))

(defn -main []
  (let [port 10001]
    (run-server ws {:port port :join? false}))
  (println "ok!"))