Fixed previous commit.

It wasn't OmniXAML ignoring the binding, the problem was that I was
trying to set the property twice.

samples/XamlTestApplicationPcl/TextBox.paml

@@ -26,8 +26,7 @@
               <Panel>
                 <TextBlock Name="watermark"
                            Opacity="0.5"
-                           Text="{TemplateBinding Watermark}"
-                           IsVisible="{TemplateBinding IsWatermarkVisible}">
+                           Text="{TemplateBinding Watermark}">
                   <TextBlock.IsVisible>
                     <Binding RelativeSource="{RelativeSource TemplatedParent}"
                              SourcePropertyPath="Text"

samples/XamlTestApplicationPcl/Views/MainWindow.paml

@@ -3,8 +3,7 @@
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:vm="clr-namespace:XamlTestApplication.ViewModels;assembly=XamlTestApplicationPcl"
         Title="Perspex Test Application" Width="800" Height="600">
-  <TextBox Watermark="Hello"></TextBox>
-    <!--<Grid RowDefinitions="Auto,*,Auto" ColumnDefinitions="*,*">
+    <Grid RowDefinitions="Auto,*,Auto" ColumnDefinitions="*,*">
         <TabControl Grid.Row="1" Grid.ColumnSpan="2" Padding="5">
             <TabControl.Transition>
                 <PageSlide Duration="0.25" />
@@ -41,7 +40,6 @@
                                Foreground="#212121" />
                     <TextBlock Text="A label capable of displaying HTML content" FontSize="13" Foreground="#727272"
                                Margin="0, 0, 0, 10" />
-                    --><!--PLEASE, FIX <HtmlLabel /> --><!--
                 </StackPanel>
             </TabItem>
             <TabItem Header="Input">
@@ -222,5 +220,5 @@
                 </Grid>
             </TabItem>
         </TabControl>
-    </Grid>-->
+    </Grid>
 </Window>