diff --git a/LehrerApp.Desktop/ViewModels/Groups/GroupViewModels.cs b/LehrerApp.Desktop/ViewModels/Groups/GroupViewModels.cs
index 37ea713..e9cba7e 100644
--- a/LehrerApp.Desktop/ViewModels/Groups/GroupViewModels.cs
+++ b/LehrerApp.Desktop/ViewModels/Groups/GroupViewModels.cs
@@ -167,6 +167,13 @@ public partial class GroupDetailViewModel : ObservableObject
     [ObservableProperty] private StudentSummary? _selectedStudent;
     [ObservableProperty] private ExamSummary? _selectedExam;
 
+    // Eigene Property statt "Group.IsDifferentiated" im Binding-Pfad: die View bindet bereits,
+    // bevor LoadGroup() läuft (siehe MainWindowViewModel.NavigateToGroupDetail), Group ist dann
+    // kurzzeitig null — ein verschachtelter Pfad würde dafür jedes Mal einen Binding-Fehler loggen.
+    public bool IsDifferentiated => Group?.IsDifferentiated ?? false;
+
+    partial void OnGroupChanged(LearningGroup? value) => OnPropertyChanged(nameof(IsDifferentiated));
+
     public ObservableCollection<StudentSummary> Students { get; } = [];
     public ObservableCollection<ExamSummary> Exams { get; } = [];
 
diff --git a/LehrerApp.Desktop/Views/Groups/GroupDetailView.axaml b/LehrerApp.Desktop/Views/Groups/GroupDetailView.axaml
index d052fab..90ff12f 100644
--- a/LehrerApp.Desktop/Views/Groups/GroupDetailView.axaml
+++ b/LehrerApp.Desktop/Views/Groups/GroupDetailView.axaml
@@ -57,7 +57,7 @@
             <DataGridTextColumn Header="Name"    Binding="{Binding FullName}"    Width="*"/>
             <DataGridTextColumn Header="Zeitraum" Binding="{Binding PeriodLabel}" Width="90"/>
             <DataGridTemplateColumn Header="Niveau" Width="130"
-                                     IsVisible="{Binding Group.IsDifferentiated}">
+                                     IsVisible="{Binding IsDifferentiated}">
               <DataGridTemplateColumn.CellTemplate>
                 <DataTemplate x:DataType="vm:StudentSummary">
                   <ComboBox ItemsSource="{x:Static vm:StudentSummary.NiveauOptions}"
@@ -110,7 +110,7 @@
               <DataGridTextColumn Header="Datum"  Binding="{Binding Date}"  Width="110"/>
               <DataGridTextColumn Header="Titel"  Binding="{Binding Title}" Width="*"/>
               <DataGridTextColumn Header="Niveau" Binding="{Binding NiveauLabel}" Width="80"
-                                   IsVisible="{Binding Group.IsDifferentiated}"/>
+                                   IsVisible="{Binding IsDifferentiated}"/>
               <DataGridTemplateColumn Header="Status" Width="150">
                 <DataGridTemplateColumn.CellTemplate>
                   <DataTemplate x:DataType="vm:ExamSummary">