Changing map to pmap in my Clojure program leads to weird exception (ClassCastException) -

as far know, pmap in clojure works map, calculates results in parallel, using futures under hood. should "just work" function , sequence, if map works them. (unless there evil side effects prevent it, in case of program there nothing more loading data http server , transforming it)
, in case pmap doesn't work expected. why can happen?

the problem arises here (if change map pmap): https://github.com/magicgoose/dvachmaster/blob/master/src/dvach/core.clj#l82

(defn thread-list   "load threads pages, trying each page @ `max-trials` times `retry-inteval`"   [board]     (try       (let [p0 (load-body (board-addr board 0))             numpages (count (:pages p0))             other-pages (map                    ; problem here                           (comp                             load-body                             (partial board-addr board))                           (range 1 numpages))             all-pages (cons p0 other-pages)             ]          (doall           ((comp (partial reduce concat) (partial map :threads)) all-pages)))       (catch throwable e         (.printstacktrace e)))) 

the exception get:

java.util.concurrent.executionexception: java.lang.classcastexception: java.lang.long cannot cast java.util.concurrent.future     @ java.util.concurrent.futuretask$sync.innerget(unknown source)     @ java.util.concurrent.futuretask.get(unknown source)     @ clojure.core$deref_future.invoke(core.clj:2108)     @ clojure.core$future_call$reify__6267.deref(core.clj:6308)     @ clojure.core$deref.invoke(core.clj:2128)     @ clojure.core$pmap$step__6280$fn__6282.invoke(core.clj:6358)     @ clojure.lang.lazyseq.sval(lazyseq.java:42)     @ clojure.lang.lazyseq.seq(lazyseq.java:60)     @ clojure.lang.rt.seq(rt.java:484)     @ clojure.core$seq.invoke(core.clj:133)     @ clojure.core$map$fn__4207.invoke(core.clj:2479)     @ clojure.lang.lazyseq.sval(lazyseq.java:42)     @ clojure.lang.lazyseq.seq(lazyseq.java:60)     @ clojure.lang.cons.next(cons.java:39)     @ clojure.lang.rt.next(rt.java:598)     @ clojure.core$next.invoke(core.clj:64)     @ clojure.core.protocols$fn__6034.invoke(protocols.clj:146)     @ clojure.core.protocols$fn__6005$g__6000__6014.invoke(protocols.clj:19)     @ clojure.core.protocols$seq_reduce.invoke(protocols.clj:27)     @ clojure.core.protocols$fn__6026.invoke(protocols.clj:53)     @ clojure.core.protocols$fn__5979$g__5974__5992.invoke(protocols.clj:13)     @ clojure.core$reduce.invoke(core.clj:6175)     @ clojure.lang.afn.applytohelper(afn.java:163)     @ clojure.lang.afn.applyto(afn.java:151)     @ clojure.core$apply.invoke(core.clj:619)     @ clojure.core$partial$fn__4190.doinvoke(core.clj:2396)     @ clojure.lang.restfn.invoke(restfn.java:408)     @ clojure.core$comp$fn__4154.invoke(core.clj:2331)     @ dvach.core$thread_list.invoke(core.clj:91)     @ dvach.core$eval3813.invoke(no_source_file:2)     @ clojure.lang.compiler.eval(compiler.java:6619)     @ clojure.lang.compiler.eval(compiler.java:6582)     @ clojure.core$eval.invoke(core.clj:2852)     @ clojure.main$repl$read_eval_print__6588$fn__6591.invoke(main.clj:259)     @ clojure.main$repl$read_eval_print__6588.invoke(main.clj:259)     @ clojure.main$repl$fn__6597.invoke(main.clj:277)     @ clojure.main$repl.doinvoke(main.clj:277)     @ clojure.lang.restfn.invoke(restfn.java:1096)     @ clojure.tools.nrepl.middleware.interruptible_eval$evaluate$fn__1023.invoke(interruptible_eval.clj:56)     @ clojure.lang.afn.applytohelper(afn.java:159)     @ clojure.lang.afn.applyto(afn.java:151)     @ clojure.core$apply.invoke(core.clj:617)     @ clojure.core$with_bindings_star_.doinvoke(core.clj:1788)     @ clojure.lang.restfn.invoke(restfn.java:425)     @ clojure.tools.nrepl.middleware.interruptible_eval$evaluate.invoke(interruptible_eval.clj:41)     @ clojure.tools.nrepl.middleware.interruptible_eval$interruptible_eval$fn__1064$fn__1067.invoke(interruptible_eval.clj:171)     @ clojure.core$comp$fn__4154.invoke(core.clj:2330)     @ clojure.tools.nrepl.middleware.interruptible_eval$run_next$fn__1057.invoke(interruptible_eval.clj:138)     @ clojure.lang.afn.run(afn.java:24)     @ java.util.concurrent.threadpoolexecutor.runworker(unknown source)     @ java.util.concurrent.threadpoolexecutor$worker.run(unknown source)     @ java.lang.thread.run(unknown source) caused by: java.lang.classcastexception: java.lang.long cannot cast java.util.concurrent.future     @ clojure.core$deref_future.invoke(core.clj:2108)     @ clojure.core$deref.invoke(core.clj:2129)     @ dvach.core$load_body.invoke(core.clj:74)     @ clojure.core$comp$fn__4154.invoke(core.clj:2331)     @ clojure.core$pmap$fn__6275$fn__6276.invoke(core.clj:6354)     @ clojure.core$binding_conveyor_fn$fn__4107.invoke(core.clj:1836)     @ clojure.lang.afn.call(afn.java:18)     @ java.util.concurrent.futuretask$sync.innerrun(unknown source)     @ java.util.concurrent.futuretask.run(unknown source)     ... 3 more 

the problem stack trace complains @max-trials on line 74; should read max-trials instead. (max-trials loop variable initialized @retry-count on line 66; it'll number then, decremented on each iteration.)

it may arise intermittently, since point in code reached if try block starting on line 68 fails fetch result.