ReactiveUI ReactiveCollection AddRange/ItemsAdded repro

MainWindow.xaml

<Window x:Class="WpfApplication3.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <StackPanel Orientation="Horizontal">
            <StackPanel Margin="5">
                <StackPanel Orientation="Horizontal">
                    <TextBlock Text="Original Count" />
                    <TextBlock Margin="5,0,0,0" Text="{Binding Col.Count}" />
                </StackPanel>
                <StackPanel Orientation="Horizontal">
                    <TextBlock Text="Manual Count" />
                    <TextBlock Margin="5,0,0,0" Text="{Binding ManualCount}" />
                </StackPanel>
                <StackPanel Orientation="Horizontal">
                    <TextBlock Text="ListBox Original Count" />
                    <TextBlock Margin="5,0,0,0" Text="{Binding Items.Count, ElementName=LB}" />
                </StackPanel>
                <TextBlock Text="Original List" />
                <ListBox Name="LB" ItemsSource="{Binding Col}">
                    <ListBox.ItemTemplate>
                        <DataTemplate>
                            <TextBlock Text="{Binding Id}" />
                        </DataTemplate>
                    </ListBox.ItemTemplate>
                </ListBox>
            </StackPanel>

            <StackPanel Margin="5">
                <StackPanel Orientation="Horizontal">
                    <TextBlock Text="Derived Count" />
                    <TextBlock Margin="5,0,0,0" Text="{Binding DerivedCol.Count}" />
                </StackPanel>
                <StackPanel Orientation="Horizontal">
                    <TextBlock Text="Manual Derived Count" />
                    <TextBlock Margin="5,0,0,0" Text="{Binding ManualDerivedCount}" />
                </StackPanel>
                <StackPanel Orientation="Horizontal">
                    <TextBlock Text="ListBox Derived Count" />
                    <TextBlock Margin="5,0,0,0" Text="{Binding Items.Count, ElementName=DerivedLB}" />
                </StackPanel>
                <TextBlock Text="Derived List" />
                <ListBox Name="DerivedLB" ItemsSource="{Binding DerivedCol}">
                    <ListBox.ItemTemplate>
                        <DataTemplate>
                            <TextBlock Text="{Binding Id}" />
                        </DataTemplate>
                    </ListBox.ItemTemplate>
                </ListBox>
            </StackPanel>

            <StackPanel Margin="5" Orientation="Horizontal">
                <TextBlock Text="Original CollectionChanged Count" />
                <TextBlock Margin="5,0,0,0" Text="{Binding CollectionChangedCount}" />
            </StackPanel>
        </StackPanel>
    </Grid>
</Window>

MainWindow.xaml.cs

using System;
using System.Collections.Specialized;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Threading;
using ReactiveUI;

namespace WpfApplication3
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            DataContext = new MainViewModel();
        }
    }

    public class Model : ReactiveObject
    {
        static int _UniqueId;
        public int Id { get; private set; }

        public Model()
        {
            Id = _UniqueId++;
        }
    }

    public class MainViewModel : ReactiveObject
    {
        ReactiveCollection<Model> _Col;
        public ReactiveCollection<Model> Col
        {
            get { return _Col; }
            set { this.RaiseAndSetIfChanged(x => x.Col, value); }
        }

        ReactiveCollection<Model> _DerivedCol;
        public ReactiveCollection<Model> DerivedCol
        {
            get { return _DerivedCol; }
            set { this.RaiseAndSetIfChanged(x => x.DerivedCol, value); }
        }

        int _CollectionChangedCount;
        public int CollectionChangedCount
        {
            get { return _CollectionChangedCount; }
            set { this.RaiseAndSetIfChanged(x => x.CollectionChangedCount, value); }
        }

        int _ManualCount;
        public int ManualCount
        {
            get { return _ManualCount; }
            set { this.RaiseAndSetIfChanged(x => x.ManualCount, value); }
        }

        int _ManualDerivedCount;
        public int ManualDerivedCount
        {
            get { return _ManualDerivedCount; }
            set { this.RaiseAndSetIfChanged(x => x.ManualDerivedCount, value); }
        }

        public MainViewModel()
        {
            // UI Thread
            Col = new ReactiveCollection<Model>();
            Col.CollectionChanged += (sender, args) => {
                if (args.Action == NotifyCollectionChangedAction.Add) CollectionChangedCount++;
            };

            DerivedCol = new ReactiveCollection<Model>();
            Col.ItemsAdded.Subscribe(x => DerivedCol.Add(x));
            Col.ItemsRemoved.Subscribe(x => DerivedCol.Remove(x));

            // Add single item - Works
            Col.Add(new Model());
            UpdateManualCounts();

            // Add range - Fails
            Col.AddRange(new[] { new Model(), new Model() });
            UpdateManualCounts();

            // Worker Thread
            Task.Factory.StartNew(() =>
            {
                while (true)
                {
                    // Add single item - Works
                    DispatcherInvoke(() => Col.Add(new Model()));

                    // Add Range - Fails in beginning, but magically starts working again
                    DispatcherInvoke(() => Col.AddRange(new[] { new Model(), new Model() }));
                    UpdateManualCounts();
                    Thread.Sleep(2000);
                }
            });
        }

        private void DispatcherInvoke(Action action)
        {
            Application.Current.Dispatcher.Invoke(action);
        }

        private void UpdateManualCounts()
        {
            ManualCount = Col.Count();
            ManualDerivedCount = DerivedCol.Count();
        }
    }
}