ClojureScript multimethod namespace reference problem

gistfile1.clj

;;ClojureScript compiler 329708 (2011.12.14)
;;Based on RangeNum protocol by Tassilo Horn:
;;    http://groups.google.com/group/clojure/browse_thread/thread/f3192b351b0ab2b4/ec6c106dfdcf0cf9?lnk=gst&q=ranged#msg_ed6de8b7a5cabf41

(ns c2.main
  (:refer-clojure :exclude [+])
  (:use-macros [c2.util :only [typeof]]))


(defprotocol RangeNumProtocol
  (check [this])
  (value [this]))

(defprotocol RangeNumLimits
  (upper [this])
  (lower [this]))

(deftype RangeNum [v l u]
  RangeNumProtocol
  (check [this]
    (if (or (> v u) (< v l))
      (throw (js/Error. "Over/Underflow"))
      this))
  (value [this] (and (check this) v))
  RangeNumLimits
  (upper [this] u)
  (lower [this] v))

(extend-protocol RangeNumProtocol
  number
  (check [this] this)
  (value [this] this))



(defmulti + #(let [x (first %&)]
               (cond
                (= "number" (typeof x))     :number
                (instance? RangeNum x)      :range_num)))

(defmethod + :number
  ([a] a)
  ([a b] (clojure.core/+ a (value b)))
  ([a b & more] (reduce + (+ a b) more)))

(defmethod + :range_num
  ([a] a)
  ([a b] (RangeNum. (value (+ (value a) b)) (lower a) (upper a)))
  ([a b & more] (reduce + (+ a b) more)))



;;Here's the problem: despite + being excluded in the namespace declaration, it still points to clojure.core/+ rather than the multimethod.
(let [x (RangeNum. 500 1 1000)]
  (+ x 100) ;;=> [object Object]100
  (clojure.core/+ x 100) ;;=> [object Object]100
  (c2.main/+ x 100) ;;=> c2.main.RangeNum
  )

Fixed here:

https://github.com/lynaghk/clojurescript/tree/114-refer-clojure-exclude