PublishSubject doesn't work with concatWith operator

[haashem]

In the below example, concatWith should emits the values added by stream 2:

void exampleOf(String of, {required void Function() action}) {
  print('\n———Example $of———');
  action();
}

exampleOf('concatWith(Iterable<Stream>)', action: () {
    final stream1 = Stream.fromIterable([2, 3, 4]);
    final stream2 = PublishSubject<int>();

    stream1.concatWith([stream2]).listen(
      (event) => print('append: $event'),
      onDone: () => print('Done'),
    );
    stream2.add(5);
    stream2.close();
  });

Expected:

———Example concatWith(Iterable<Stream>)———
append: 2
append: 3
append: 4
append: 5
Done

Actual:

———Example concatWith(Iterable<Stream>)———
append: 2
append: 3
append: 4
Done

But if I replace PublishSubject with BehaviorSubject it works as expected.
I think it's a bug.

[hoc081098]

all elements from stream1 will be delivered to the result stream with microtask delays (async by default).

At this time, adding value to PublishSubject is ignored, because the stream1 is listening.

stream1: --2--3--4--|
stream2: 5
result     : --2--3--4--|

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[hoc081098]

See https://github.com/ReactiveX/rxdart?tab=readme-ov-file#rx-observables-vs-dart-streams, and https://api.flutter.dev/flutter/dart-async/Stream-class.html for more details

A source of asynchronous data events.