NumericUpDown Undo/Redo Value-Binding not updated

[TZM-svat]

Description
Using Undo/Redo (Ctrl+Z / Ctrl+Y) works correctly while NumericUpDown has the initial focus. After losing focus once and refocusing the control, Undo/Redo only changes the displayed value but the binded property is never updated. After losing focus again the displayed value returns to the unchanged binded property value.

To Reproduce
MainWindow:

<Window x:Class="WpfMahAppsNumericUpDown.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfMahAppsNumericUpDown"
        xmlns:mah="http://metro.mahapps.com/winfx/xaml/controls"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="2*" />
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            <RowDefinition Height="Auto" />
            <RowDefinition Height="Auto" />
            <RowDefinition Height="30" />
            <RowDefinition Height="Auto" />
            <RowDefinition Height="Auto" />
            <RowDefinition Height="Auto" />
        </Grid.RowDefinitions>

        <TextBlock Text="NumericUpDown" FontWeight="Bold" Grid.Row="0" Grid.Column="0" Grid.ColumnSpan="2" Margin="0,0,0,10"/>

        <TextBlock Text="Value" Grid.Row="1" Grid.Column="0" />
        <mah:NumericUpDown Value="{Binding NumericUpDownValue, UpdateSourceTrigger=PropertyChanged}" Grid.Row="1" Grid.Column="1" />

        <TextBlock Text="Read only" Grid.Row="2" Grid.Column="0" />
        <mah:NumericUpDown Value="{Binding NumericUpDownValue, UpdateSourceTrigger=PropertyChanged}" Grid.Row="2" Grid.Column="1"
                 IsReadOnly="True" />

        <TextBlock Text="TextBox" FontWeight="Bold" Grid.Row="4" Grid.Column="0" Grid.ColumnSpan="2" Margin="0,0,0,10"/>

        <TextBlock Text="Value" Grid.Row="5" Grid.Column="0"/>
        <TextBox Text="{Binding TextBoxValue, UpdateSourceTrigger=PropertyChanged}" Grid.Row="5" Grid.Column="1"/>

        <TextBlock Text="Read only" Grid.Row="6" Grid.Column="0"/>
        <TextBox Text="{Binding TextBoxValue, UpdateSourceTrigger=PropertyChanged}" Grid.Row="6" Grid.Column="1" IsReadOnly="True"/>
    </Grid>
</Window>

ViewModel:

    public class MainWindowViewModel : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;
        private double _numericUpDownValue;
        private double _textBoxValue;

        public MainWindowViewModel()
        {
            NumericUpDownValue = 5;
            TextBoxValue = 5;
        }

        public double NumericUpDownValue
        {
            get => _numericUpDownValue;
            set
            {
                if (Math.Abs(_numericUpDownValue - value) < double.Epsilon) return;
                _numericUpDownValue = value;
                OnPropertyChanged(nameof(NumericUpDownValue));
            }
        }
        public double TextBoxValue
        {
            get => _textBoxValue;
            set
            {
                if (Math.Abs(_textBoxValue - value) < double.Epsilon) return;
                _textBoxValue = value;
                OnPropertyChanged(nameof(TextBoxValue));
            }
        }

        protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }

Steps to reproduce the behavior:

1. Change value in NumericUpDown
2. Click other control to lose focus
3. Click NumericUpDown to get focus again and press Ctrl+Z (Second control with same Binding is not updated)
4. Click other control to lose focus again (First control reverts back to binded value)
5. Do the same with the default TextBox controls -> everything works

Expected behavior
The Undo/Redo commands should always correctly change the binded property like the default TextBox already does.

Screenshots

Environment:

• MahApps.Metro version 1.6.5
• .NET Framework 4.6.2

Repo
https://github.com/TZM-svat/MahAppsNumericUpDown.git