BUG: RefCount with MinObservers > 1 Behaves Unexpectedly

[mikeronayne]

Code

Subject<int> subj = new();

var refCount = subj.Publish().RefCount(minObservers: 2);

subj.OnNext(1);

var sub1 = refCount.Subscribe(c => Console.WriteLine($"sub1: {c}"));

subj.OnNext(2);

var sub2 = refCount.Subscribe(c => Console.WriteLine($"sub2: {c}"));

subj.OnNext(3);

sub1.Dispose();

subj.OnNext(4);

var sub3 = refCount.Subscribe(c => Console.WriteLine($"sub3: {c}"));

subj.OnNext(5);

var sub4 = refCount.Subscribe(c => Console.WriteLine($"sub4: {c}"));

subj.OnNext(6);

sub2.Dispose();

sub3.Dispose();

sub4.Dispose();

Expected Output

I would expect not to receive values until sub2 has subscribed. Then I would expect not to receive values after sub1 is disposed. Then I would expect to receive values again after sub3 has subscribed.

sub1: 3
sub2: 3
sub2: 5
sub3: 5
sub2: 6
sub3: 6
sub4: 6

Actual Output

1. sub2 should not have received value 4 since we were below minObservers at that point.
2. Definitely shouldn't have gotten an exception on sub3 subscribing.

sub1: 3
sub2: 3
sub2: 4

InvalidOperationException: Disposable has already been assigned.
at System.Reactive.Disposables.SingleAssignmentDisposableValue.set_Disposable(IDisposable value) 
at System.Reactive.Linq.ObservableImpl.RefCount`1.Eager._.Run()   at System.Reactive.Linq.ObservableImpl.RefCount`1.Eager.Run(_ sink) 
at System.Reactive.Producer`2.<>c.<SubscribeRaw>b__1_0(ValueTuple`2 tuple) 
at System.Reactive.Concurrency.Scheduler.<>c__75`1.<ScheduleAction>b__75_0(IScheduler _, ValueTuple`2 tuple)
at System.Reactive.Concurrency.CurrentThreadScheduler.Schedule[TState](TState state, TimeSpan dueTime, Func`3 action)
at System.Reactive.Concurrency.LocalScheduler.Schedule[TState](TState state, Func`3 action)
at System.Reactive.Concurrency.Scheduler.ScheduleAction[TState](IScheduler scheduler, TState state, Action`1 action)
at System.Reactive.Producer`2.SubscribeRaw(IObserver`1 observer, Boolean enableSafeguard)
at System.Reactive.Producer`2.Subscribe(IObserver`1 observer)
at System.ObservableExtensions.Subscribe[T](IObservable`1 source, Action`1 onNext)   at UserQuery.Main(), line 21

If this IS expected and not a bug, would love an explanation of what I'm misunderstanding. Thank you!