Multimethods bug

multi.clj

(defmulti foo (fn [x] x))
;=> #<[object Object]>
(defmethod foo ::a [x] "a!")
;=> #<[object Object]>

; Hierarchy setting
(derive ::a1 ::a)
;=> nil

; works well
(foo ::a1)
;=> "a!"

;; add another method
(defmethod foo ::b [x] "b!")
;=> #<[object Object]>

; error!
(foo ::a1)
; "Error evaluating:" (foo :cljs.user/a1) :as "cljs.user.foo.call(null,\"?'cljs.user/a1\");\n"
; #<Error: No method in multimethod 'function name(x){
; if(cljs.core.truth_(cljs.core.string_QMARK_.call(null,x)))
; {return x;
; } else
; {if(cljs.core.truth_((function (){var or__3548__auto____7059 = cljs.core.keyword_QMARK_.call(null,x);
; 
; if(cljs.core.truth_(or__3548__auto____7059))
; {return or__3548__auto____7059;
; } else
; {return cljs.core.symbol_QMARK_.call(null,x);
; }
; })()))
; {var i__7060 = x.lastIndexOf("/");
; 
; if(cljs.core.truth_((i__7060 < 0)))
; {return cljs.core.subs.call(null,x,2);
; } else
; {return cljs.core.subs.call(null,x,(i__7060 + 1));
; }
; } else
; {if(cljs.core.truth_("?'else"))
; {throw (new Error(cljs.core.str.call(null,"Doesn't support name: ",x)));
; } else
; {return null;
; }
; }
; }
; }' for dispatch value: ?'cljs.user/a1>
; Error: No method in multimethod 'function name(x){
; if(cljs.core.truth_(cljs.core.string_QMARK_.call(null,x)))
; {return x;
; } else
; {if(cljs.core.truth_((function (){var or__3548__auto____7059 = cljs.core.keyword_QMARK_.call(null,x);
; 
; if(cljs.core.truth_(or__3548__auto____7059))
; {return or__3548__auto____7059;
; } else
; {return cljs.core.symbol_QMARK_.call(null,x);
; }
; })()))
; {var i__7060 = x.lastIndexOf("/");
; 
; if(cljs.core.truth_((i__7060 < 0)))
; {return cljs.core.subs.call(null,x,2);
; } else
; {return cljs.core.subs.call(null,x,(i__7060 + 1));
; }
; } else
; {if(cljs.core.truth_("?'else"))
; {throw (new Error(cljs.core.str.call(null,"Doesn't support name: ",x)));
; } else
; {return null;
; }
; }
; }
; }' for dispatch value: ?'cljs.user/a1
;     at do_invoke (http://localhost:8080/cljs/cljs/core.js:11186:9)
;     at [object Object].cljs$core$IMultiFn$_invoke (http://localhost:8080/cljs/cljs/core.js:11283:28)
;     at _invoke (http://localhost:8080/cljs/cljs/core.js:11162:12)
;     at [object Object].<anonymous> (http://localhost:8080/cljs/cljs/core.js:11287:26)
;     at [object Object].call (http://localhost:8080/cljs/cljs/core.js:11294:26)
;     at eval at <anonymous> (http://localhost:8080/cljs/clojure/browser/repl.js:21:158)
;     at eval at <anonymous> (http://localhost:8080/cljs/clojure/browser/repl.js:21:158)
;     at http://localhost:8080/cljs/clojure/browser/repl.js:21:153
;     at evaluate_javascript (http://localhost:8080/cljs/clojure/browser/repl.js:33:3)
;     at Object.callback (http://localhost:8080/cljs/clojure/browser/repl.js:115:126)
; nil