WPF Datepicker shows the content of a nearby Textblock - wpf

Question

anybody got an idea why the datepicker shows the content of a nearby label? The label which is displayed is in a different grid. When I delete the Labels text and leave it blank the text of the next label of the grid is displayed and so on.
Cant figure out why this happens. Once im hovering over the datepicker with the mouse it shows the correct watermark.
[EDIT] Sorry, following a part of the code.
<StackPanel Grid.Row="1" Grid.Column="0">
<Grid Margin="10,10,0,0">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<Label Content="Beauftragt durch:"
Grid.Row="0" Grid.Column="0"
Width="110" Margin="10,2"
HorizontalAlignment="Left" />
<TextBox x:Name="OrderedByEmp"
IsEnabled="False"
Text="{Binding OrderedByEmpName}"
Grid.Row="0" Grid.Column="1"
Width="110" Margin="10,2"
/>
<Label Content="Projekt:"
Grid.Row="1" Grid.Column="0"
Width="110" Margin="10,2"
HorizontalAlignment="Left" />
<TextBox x:Name="Project"
MaxLength="10"
Text="{Binding Project}"
Grid.Row="1" Grid.Column="1"
Width="110" Margin="0,2"
/>
<Label Content="Auftrag:"
Grid.Row="2" Grid.Column="0"
Width="110" Margin="10,2"
HorizontalAlignment="Left" />
<TextBox x:Name="Order" Text="{Binding Commission}"
MaxLength="8"
Grid.Row="2" Grid.Column="1"
Width="110" Margin="0,2"
/>
</Grid>
</StackPanel>
<StackPanel Grid.Row="1" Grid.Column="1">
<Grid Margin="10,10,0,0">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="Auto"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<Label Content="Erstellt am:"
Grid.Row="0" Grid.Column="0"
Width="110" Margin="10,2"
HorizontalAlignment="Left" />
<TextBox x:Name="OrderDate" Text="{Binding OrderDate, Mode=TwoWay,StringFormat='{}{0:dd.MM.yyyy}'}"
IsEnabled="False"
Grid.Row="0" Grid.Column="1"
Width="110" Margin="0,2"
/>
<Label Content="Benötigt bis:"
Grid.Row="1" Grid.Column="0"
Width="110" Margin="10,2"
HorizontalAlignment="Left" />
<DatePicker x:Name="ExpectedFinishDate"
Grid.Row="1" Grid.Column="1"
Width="110"></DatePicker>
<Label Content="Abteilung:"
Grid.Row="2" Grid.Column="0"
Width="110" Margin="10,2" />
<ComboBox x:Name="Departments" Grid.Row="2" Grid.Column="1">
<ComboBox.ItemTemplate>
<DataTemplate>
<Label Content="{Binding Bezeichnung}" />
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
</Grid>
</StackPanel>
<StackPanel Grid.Column="2" Grid.Row="1">
<Grid Margin="10,10,2,2">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="Auto"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="*"/>
<RowDefinition Height="*"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<TextBlock Grid.Row="0" Grid.Column="0"
VerticalAlignment="Center" HorizontalAlignment="Right">
FLAG:
</TextBlock>
<Image Grid.Row="0" Grid.Column="1" Height="20" Source="/Pictures/NotStartetButton.png" />
<Label Content="Fertiggestellt am:"
Grid.Row="1" Grid.Column="0"
Width="110" Margin="10,2"
HorizontalAlignment="Left" />
<TextBox x:Name="FinishDatetime"
IsEnabled="False"
Grid.Row="1" Grid.Column="1"
Width="110" Margin="0,2"
/>
<Label Content="Fertiggestellt durch"
Grid.Row="2" Grid.Column="0"
Width="110" Margin="10,2"
HorizontalAlignment="Left" />
<TextBox x:Name="FinishedByEmp"
IsEnabled="False"
Grid.Row="2" Grid.Column="1"
Width="110" Margin="0,2"
/>
</Grid>
</StackPanel>
When I put the datepicker to another spot its working correct.
Tried now for hours to figure out why... but cant find the reason.
Thanks for any suggestion!

Answer 1

I've tried to reproduce the problem in another file and realized that the behavior has changed. Stupidly I left the further research on that problem since I've thought it's located anywhere in the related bindings and just went ahead to come back to that later.
But finally I made so many changes that the problem just disappeared.