RxJava 2.1.0+withLatestFrom+cache+firstOrError causes NoSuchElementException

RxJavaTest.java

    @Test
    fun withLatestFromCausesNoSuchElementException() {
        val state = Observable.just(42).cacheWithInitialCapacity(1)
        var error = 0
        val threads = (0..4 - 1)
                .map {
                    Thread {
                        Observable.just(Unit)
                                .withLatestFrom(state, BiFunction { _: Unit, state: Int -> state })
                                .firstOrError()
                                .subscribe({}, { if (it is NoSuchElementException) error++ })
                    }
                }
        threads.forEach { it.start() }
        threads.forEach { it.join() }
        assertThat(error, Matchers.greaterThan(0))
    }

원인은 모르겠지만 combineLatest로 바꾸거나 state를 먼저 단일 쓰레드에서 subscribe 해주면 피할 수 있어요.