Grid rows aren't the (relative) height I set them to - wpf

Question

I was working on a UserControl in a View, when I came across this problem:
I set my content grids row heights to be 2*, 1* and 1* with the lines in between set to auto.
Now. The uppermost row has a grid nested in with a TextBlock and a TextBox. The height of the cell is in no way 2*. It looks like it would look if I had set it to auto. I'm pretty sure the other 2 content rows (containing buttons) are the right height either.
Now I hope you guys can help me fix this. I've googled around a bit and I can't seem to find a fitting solution.
Here's the code:
<Grid Margin="5">
<Grid.RowDefinitions>
<RowDefinition Height="2*"/>
<RowDefinition Height="auto"/>
<RowDefinition Height="1*"/>
<RowDefinition Height="auto"/>
<RowDefinition Height="1*"/>
</Grid.RowDefinitions>
<Grid>
<Grid.RowDefinitions>
<RowDefinition/>
<RowDefinition/>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="auto" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<TextBlock Name="TBCustomerTitle" Margin="0,0,8,0" FontWeight="Bold"
Visibility="{Binding SetVisibility, UpdateSourceTrigger=PropertyChanged}">Customer:</TextBlock>
<TextBox Name="TBCustomerData" Grid.Column="1"
Visibility="{Binding SetVisibility, UpdateSourceTrigger=PropertyChanged}"
Text="{Binding DisplayedCustomer.Name, UpdateSourceTrigger=PropertyChanged}"></TextBox>
</Grid>
<Line Grid.Row="1" Style="{StaticResource horizontalLineStyle}" />
<StackPanel Grid.Row="2" Orientation="Vertical">
<Button Command="{Binding AddCommand}">Add a new customer</Button>
<Button Command="{Binding UpdateCommand}">Update the selected customer</Button>
<Button Command="{Binding DeleteCommand}">Delete the selected customer</Button>
</StackPanel>
<Line Grid.Row="3" Style="{StaticResource horizontalLineStyle}" />
<StackPanel Grid.Row="4" Orientation="Vertical">
<Button Command="{Binding RefreshCommand}">Refresh the list</Button>
<Button Command="{Binding ClearSelectionCommand}">Clear selection</Button>
</StackPanel>
</Grid>
EDIT: Now with screenshot, as requested. It's the right column I'm talking about (So yes, this UserControl is in itself another nested Grid)
EDIT 2: Here's the containing code. My page consist of three classess.
The 1st (ApplicationView.xaml) is a Window. It has the navigation buttons in the left column, a nice line, and one column containing the view of that specific object. It has no rows.
ApplicationView.xaml
<Grid>
<Grid.Resources>
<ResourceDictionary Source="StylesRD.xaml" />
</Grid.Resources>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="1*" />
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="6*" />
</Grid.ColumnDefinitions>
<!-- A DockPanel for the Navigation Buttons-->
<DockPanel Grid.Column="0" Margin="0,20" VerticalAlignment="Top" HorizontalAlignment="Center">
<ItemsControl ItemsSource="{Binding PageViewModels}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<Button Content="{Binding Name}"
Command="{Binding DataContext.ChangePageCommand, RelativeSource={RelativeSource AncestorType={x:Type Window}}}"
CommandParameter="{Binding }"
Margin="2,5"/>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</DockPanel>
<Line Grid.Column="1" Style="{StaticResource verticalLineStyle}" />
<ContentControl Grid.Column="2" Content="{Binding CurrentPageViewModel}" />
</Grid>
The view (CustomerView.xaml) is the 2nd file. It is a User control and it also has 3 columns, one with the list of Customers in this case, one for the beautiful seperating line (it is beautiful, right? /sarcasm) and the one I'm struggling with right now with the details and the buttons to do stuff.
Here also no rows.
CustomerView.xaml
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="2*" />
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="1*" />
</Grid.ColumnDefinitions>
<!-- Customer list -->
<view:CustomerListView Grid.Column="0" VerticalAlignment="Top"/>
<Line Grid.Column="1" Style="{StaticResource verticalLineStyle}" />
<!-- Details -->
<view:CustomerDetailsView Grid.Column="2" VerticalAlignment="Top"/>
</Grid>

Answer 1

Your inner Grid has two RowDefinitions without a height setting. Therefore the default Height="*" will be used for both rows. Your inner grid doesn't need two RowDefinitions, so removing them should fix your issue. So your inner grid definition should look like this:
<Grid>
<!--
remove these row definitions
<Grid.RowDefinitions>
<RowDefinition/>
<RowDefinition/>
</Grid.RowDefinitions>
-->
<Grid.ColumnDefinitions>
<ColumnDefinition Width="auto" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<TextBlock Name="TBCustomerTitle" Margin="0,0,8,0" FontWeight="Bold"
Visibility="{Binding SetVisibility, UpdateSourceTrigger=PropertyChanged}">Customer:</TextBlock>
<TextBox Name="TBCustomerData" Grid.Column="1"
Visibility="{Binding SetVisibility, UpdateSourceTrigger=PropertyChanged}"
Text="{Binding DisplayedCustomer.Name, UpdateSourceTrigger=PropertyChanged}"></TextBox>
</Grid>
Edit:
It works for me as expected. The TextBox and TextBlock get stretched to 2* height, and the two StackPanels have a height of 1* each. Please provide the XAML where you use your user control. Seems like there lies the problem.
Edit 2:
Ah, now I see it. The VerticalAlignment="Top" setting in your CustomerView.xaml pushes your CustomerDetailsView to the top. Either remove this attribute or set the VerticalAlignment to Stretch.

Answer 2

The xaml you provided is working fine, the problem is in the containing xaml. Look at this example xaml.
<StackPanel Orientation="Horizontal">
<Border Background="Yellow">
<local:MyUserControl/>
</Border>
<StackPanel Background="Green">
<local:MyUserControl/>
</StackPanel>
</StackPanel>
And the usercontrol (stripped away bindings and styles)
<UserControl x:Class="WpfApplication3.MyUserControl"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:local="clr-namespace:WpfApplication3"
mc:Ignorable="d">
<Grid Margin="5">
<Grid.RowDefinitions>
<RowDefinition Height="2*"/>
<RowDefinition Height="auto"/>
<RowDefinition Height="1*"/>
<RowDefinition Height="auto"/>
<RowDefinition Height="1*"/>
</Grid.RowDefinitions>
<Grid>
<Grid.RowDefinitions>
<RowDefinition/>
<RowDefinition/>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="auto" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<TextBlock Name="TBCustomerTitle" Margin="0,0,8,0" FontWeight="Bold" >Customer:</TextBlock>
<TextBox Name="TBCustomerData" Grid.Column="1" Text="{Binding DisplayedCustomer.Name, UpdateSourceTrigger=PropertyChanged}"></TextBox>
</Grid>
<Line Grid.Row="1" Height="5"/>
<StackPanel Grid.Row="2" Orientation="Vertical">
<Button Command="{Binding AddCommand}">Add a new customer</Button>
<Button Command="{Binding UpdateCommand}">Update the selected customer</Button>
<Button Command="{Binding DeleteCommand}">Delete the selected customer</Button>
</StackPanel>
<Line Grid.Row="3" Height="5"/>
<StackPanel Grid.Row="4" Orientation="Vertical">
<Button Command="{Binding RefreshCommand}">Refresh the list</Button>
<Button Command="{Binding ClearSelectionCommand}">Clear selection</Button>
</StackPanel>
</Grid>
</UserControl>
As you can see the usercontrol located in the stackpanel is not stretching because stackpanel does not stretch it's contents.