tap doesnt work for the second channel if already closed

tap.clj

(require '[clojure.core.async :refer (<!! >!! close! chan mult tap alt!! timeout)])

(defn assert-closed! [c m] (assert (= nil (alt!! c ([v] v) (timeout 50) ([_] :timeout))) m))

(let [[c1 c2 c3] (repeatedly 3 chan)
      _ (close! c1)
      m (mult c1)]
  (tap m c2)
  (<!! (timeout 50))
  (tap m c3)
  (<!! (timeout 50))
  (assert-closed! c1 "c1 sanity")
  (assert-closed! c1 "c2 should")
  (assert-closed! c3 "c3 test") ; So this assert fails because tap doesn't check to see if mult-source is already closed.
  )