public class BrushNullable : IValueConverter
	{
		public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
		{
			return new SolidBrush(System.Drawing.Color.Aqua);
		}

		public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
		{
			throw new NotImplementedException();
		}
	}

<Window.Resources>
  <SolidColorBrush Color="#89ABCD" x:Key="Brush"/>
</Window.Resources>
<Grid>
  <Grid.RowDefinitions>
    <RowDefinition />
    <RowDefinition />
    <RowDefinition Height="Auto"/>
  </Grid.RowDefinitions>
  <Border
    x:Name="Border1"
    VerticalAlignment="Stretch"
    HorizontalAlignment="Stretch"
    Margin="20"
    Background="{StaticResource Brush}" />
  <wpftest2:MyBorder
    x:Name="Border2"
    Grid.Row="1"
    VerticalAlignment="Stretch"
    HorizontalAlignment="Stretch"
    Margin="20"
    Background="{Binding Source={StaticResource Brush}}"
    SomeOtherBackground="{StaticResource Brush}"/> <!-- Ok -->
  <Button
    Grid.Row="2"
    VerticalAlignment="Center"
    HorizontalAlignment="Center"
    Margin="10"
    Padding="5"
    Content="Test"
    Click="ButtonClick" />
</Grid>

public partial class MainWindow
{
  public MainWindow()
  {
    InitializeComponent();
  }

  void ButtonClick(object sender, RoutedEventArgs e)
  {
    var b1 = BindingOperations.GetBinding(Border1, Border.BackgroundProperty);
    Console.WriteLine("Binding of {{StaticResource Brush}}: {0}", b1 ?? (object)"null");
    var b2 = BindingOperations.GetBinding(Border2, Border.BackgroundProperty);
    Console.WriteLine("Binding of {{Binding Source={{StaticResource Brush}}}}: {0}", b2 ?? (object)"null");
  }
}

public class MyBorder : Border
{
  public Brush SomeOtherBackground { get; set; }
}

Binding of {StaticResource Brush}: null
Binding of {Binding Source={StaticResource Brush}}: System.Windows.Data.Binding