weird async behavior

(require '[clojure.core.async :as async])
(def c (async/to-chan (range 10)))

(async/<!! (async/filter< even? c)) ;; => 0
(async/<!! (async/filter< even? c)) ;; => 4
(async/<!! (async/filter< even? c)) ;; => 8

(let [c (async/to-chan (range 10)) evens (async/filter< even? c) odds (async/filter< odd? c)]
  (printf "first even: %d\nsecond even: %d\n" (async/<!! evens) (async/<!! evens))
  (printf "first odd: %d\nsecond odd: %d\n" (async/<!! odds) (async/<!! odds))
  (printf "third even: %d\n" (async/<!! evens)))

;; output:
;; first even: 2
;; second even: 4
;; first odd: 3
;; second odd: 7
;; third even: 6