+combineLatest:reduce: serialization issue.

gistfile1.m

for(id<RACSignal> signal in signals) {
  RACDisposable *disposable = [signal subscribe:[RACSubscriber subscriberWithNext:^(id x) {
    @synchronized(lastValues) {
      [lastValues setObject:x ? : [RACTupleNil tupleNil] forKey:[NSString stringWithFormat:@"%p", signal]];

      if(lastValues.count == signals.count) {
        NSMutableArray *orderedValues = [NSMutableArray arrayWithCapacity:signals.count];
        for(id<RACSignal> o in signals) {
          [orderedValues addObject:[lastValues objectForKey:[NSString stringWithFormat:@"%p", o]]];
        }

        if (reduceBlock == NULL) {
          [subscriber sendNext:[RACTuple tupleWithObjectsFromArray:orderedValues]];
        } else {
          [subscriber sendNext:[RACBlockTrampoline invokeBlock:reduceBlock withArguments:orderedValues]];
        }
      }
    }
  } error:^(NSError *error) {
    [subscriber sendError:error];
  } completed:^{
    @synchronized(completedSignals) {
      [completedSignals addObject:signal];
      if(completedSignals.count == signals.count) {
        [subscriber sendCompleted];
      }
    }
  }]];

  if(disposable != nil) {
    [disposables addObject:disposable];
  }
}