CreateDerivedCollection Filter Doesn't Work

So I was following the sample code on the ReactiveUI website: https://reactiveui.net/docs/handbook/collections/derived-lists and trying to create a derived list with a filter.

I am expecting that the VisibleTiles list on TweetsListViewModel will only show TweetTileViewModel's where IsHidden = false.

The first TweetTileViewModel I add to the TweetTiles list appears in the VisibleTiles list which is expected since IsHidden = false. However, after I change the IsHidden property to true, the object remains in the VisibleTiles list while I would expect it to be removed. Here is the code from the ReactiveUI site and my unit test code:

```

public class TweetDerivedCollectionTests
{
    [Fact()]
    [Trait("Category", "Instant")]
    public void MethodName()
    {
        var sut = new TweetsListViewModel();
        sut.Tweets.Add(new Tweet());

        sut.Tweets.Count.ShouldBe(1);
        sut.TweetTiles.Count.ShouldBe(1);
        sut.VisibleTiles.Count.ShouldBe(1);

        sut.TweetTiles[0].IsHidden = true;
        sut.Tweets.Count.ShouldBe(1);
        sut.TweetTiles.Count.ShouldBe(1);
        sut.VisibleTiles.Count.ShouldBe(0); //This line fails.
    }
}

public class Tweet
{
    public DateTime CreatedAt { get; set; } = DateTime.Now;
}

public class TweetTileViewModel : ReactiveObject
{
    bool isHidden;
    public bool IsHidden
    {
        get { return isHidden; }
        set { this.RaiseAndSetIfChanged(ref isHidden, value); }
    }

    public Tweet Model { get; set; }
}

public class TweetsListViewModel : ReactiveObject
{
    public ReactiveList<Tweet> Tweets = new ReactiveList<Tweet>();

    public IReactiveDerivedList<TweetTileViewModel> TweetTiles;
    public IReactiveDerivedList<TweetTileViewModel> VisibleTiles;

    public TweetsListViewModel()
    {
        TweetTiles = Tweets.CreateDerivedCollection(
            x => new TweetTileViewModel() { Model = x },
            x => true,
            (x, y) => x.Model.CreatedAt.CompareTo(y.Model.CreatedAt));

        VisibleTiles = TweetTiles.CreateDerivedCollection(
            x => x,
            x => !x.IsHidden);
    }
}

```

Am I misunderstanding the functionality of CreateDerivedCollection here or not doing something necessary to trigger the expected behavior?

For what it's worth, I have tested this code in both ReactiveUI versions 7.4.0 and the latest 8.0.0-alpha0117 and both versions exhibit the same behavior.

Thanks!