I'm using .NET 4.0 (not .NET 4.0 CP) and have run into this kinda unique issue. I created a ListBox to display bound elements, first off here is (a part) of my XAML.
<Grid Grid.Row="2" Background="#EEEEEE">
<Border Margin="6,10,10,10" BorderBrush="#666666" BorderThickness="1">
<ListBox ItemsSource="{Binding}" Name="appList" BorderThickness="0" HorizontalContentAlignment="Stretch" HorizontalAlignment="Stretch">
<ItemsControl.ItemTemplate>
<DataTemplate>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="80" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<Border Grid.Column="0" Margin="5" BorderThickness="3" CornerRadius="2" BorderBrush="Black" HorizontalAlignment="Left" VerticalAlignment="Top" x:Name="ItemBorder">
<Image Width="64" Height="64" Source="{Binding Path=IconUri}" Stretch="UniformToFill" />
</Border>
<StackPanel Margin="0,5,5,5" Grid.Column="1" Orientation="Vertical" HorizontalAlignment="Stretch">
<TextBlock FontSize="18" Text="{Binding Path=DisplayName}" />
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*" />
<ColumnDefinition Width="60"/>
</Grid.ColumnDefinitions>
<ProgressBar Grid.Column="0" Height="24" HorizontalAlignment="Stretch" IsIndeterminate="{Binding Path=IsDiscovering}" Value="{Binding Path=PercentageDownloaded}" />
<TextBlock Grid.Column="1" HorizontalAlignment="Center" VerticalAlignment="Center"><TextBlock x:Name="percentageDownloaded" /><TextBlock x:Name="percentageMeter">%</TextBlock></TextBlock>
</Grid>
</StackPanel>
</Grid>
<DataTemplate.Triggers>
<DataTrigger Binding="{Binding Path=IsDiscovering}">
<DataTrigger.Value>True</DataTrigger.Value>
<Setter TargetName="percentageDownloaded" Property="Text" Value="N/A" />
<Setter TargetName="percentageMeter" Property="Visibility" Value="Collapsed" />
</DataTrigger>
<DataTrigger Binding="{Binding Path=IsDiscovering}">
<DataTrigger.Value>False</DataTrigger.Value>
<Setter TargetName="percentageDownloaded" Property="Text" Value="{Binding Path=PercentageDownloaded}" />
<Setter TargetName="percentageMeter" Property="Visibility" Value="Visible" />
</DataTrigger>
</DataTemplate.Triggers>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ListBox>
</Border>
</Grid>
Sizing the window up stretches the ListBox content just fine, but when I size it down, it retains it's width and spawns vertical scrollbars.
