Opening context menu makes the tabcontrol items datacontext null

[qqdown]

When I created a TabControl with the original control style and right-clicked to open a context menu, everything works fine.

However, when I applied the MaterialDesigin theme and did the same operation, the DataContext of TabControl's items become null.

The startup view:

Then I right-clicked the textbox and opened the context menu, the tab item contents were gone:

From the visual hierarchy view, I found the DataContext of the TextBox was changed from ViewModel to null. If I add a DataContextChanged event to the TextBox, the event will be fired.

Before right click:

After right click:

The DataContext become null and the TextBox's content went empty, but why DataCotext changed?

Is there something I did incorrectly?

Here is the code:

MainWindows.xaml.cs

 public class ViewModel : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        private string _Name;
        public string Name
        {
            get => _Name; set { _Name = value; OnPropertyChanged("Name"); }
        }

        private void OnPropertyChanged(string name)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
        }
    }

    public partial class MainWindow : Window
    {
        public ObservableCollection<ViewModel> ViewModels { get; set; } = new ObservableCollection<ViewModel>();

        public MainWindow()
        {
            InitializeComponent();
            ViewModels.Add(new ViewModel() { Name = "aaaa" });
            ViewModels.Add(new ViewModel() { Name = "bbbb" });
            DataContext = this;
        }
    }

MainWindow.cs

<TabControl ItemsSource="{Binding ViewModels}" SelectedIndex="0">
            <TabControl.ItemTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding Name}"/>
                </DataTemplate>
            </TabControl.ItemTemplate>
            <TabControl.ContentTemplate>
                <DataTemplate>
                    <TextBox Text="{Binding Name, UpdateSourceTrigger=PropertyChanged}"/>
                </DataTemplate>
            </TabControl.ContentTemplate>
        </TabControl>

[nicolaihenriksen]

@qqdown I just had a brief look at this. I can quite easily reproduce it in the demo app, and something seems to be really strange. I need to dig a bit deeper, but it seems if you set HorizontalContentAlignment="Left" (or Right) on the TabControl, the issue seems to disappear.

The issue seems to occur when a new "window" opens; this can either be a ToolTip or a ContextMenu.
Shown below in the demo tool (with HorizontalContentAlignment temporarily removed), where the content disappears after simply hovering an element with a ToolTip:

[nicolaihenriksen]

@qqdown I created an issue for this. It is easily reproducible, even with a UI test, so this is something that needs to be fixed I believe. The issue is here: #2983

[nicolaihenriksen]

@qqdown The issue has been fixed. You can grab one of the nightly builds and verify it if you want.