Having Trouble Styling and Editing AvalonDock Document Tab Panel - wpf

Question

I'm trying to figure out how to make the VS2010 style for AvalonDock to function a little more like VS2010. The problem that I'm running into is that when there are more tabs than can fit in the header area there is no indication to the user that there are more tabs.
I thought that the tab headers were just clipped and not visible. I have a custom copy of the VS2010 style and went to the DocumentPane style:
<!--DocumentPane-->
<Style x:Key="{x:Type ad:DocumentPane}" TargetType="{x:Type ad:DocumentPane}"> ...
And found the tab headers (I think) as a "ad:DocumentTabPanel". I wrapped this in a ScrollViewer:
<ScrollViewer Style="{StaticResource ResourceKey=TabHeaderScrollViewer}" CanContentScroll="True">
<ad:DocumentTabPanel
x:Name="paneTabsPanel"
Panel.ZIndex ="1"
IsItemsHost="True"
TabItemStyle="{StaticResource CustomDocumentTabItemStyle}"/>
</ScrollViewer>
The scroll viewer is setup to have a custom style on it:
<Style x:Key="TabHeaderScrollViewer" TargetType="ScrollViewer">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="ScrollViewer">
<Grid Background="{TemplateBinding Background}">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
<ColumnDefinition Width="Auto"/>
</Grid.ColumnDefinitions>
<RepeatButton Command="ScrollBar.PageLeftCommand"></RepeatButton>
<ScrollContentPresenter Grid.Column="1"
x:Name="ScrollContentPresenter"
Cursor="{TemplateBinding Cursor}"
Margin="{TemplateBinding Padding}"
ContentTemplate="{TemplateBinding ContentTemplate}"/>
<RepeatButton Grid.Column="2" Command="ScrollBar.PageRightCommand"></RepeatButton>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
The problem I am having is that even when I load up a ton of tabs the scrolling doesn't work. I don't think this is an issue with my styling. It appears that the tab headers aren't in the VisualTree or have a collapsed visibility. I've been going through the AvalonDock source for a while, but I can't see how the headers are hidden.
I've already had to subclass some of the AvalonDock classes because I needed additional properties on them.
Can someone either explain/help me come up with a solution to scroll the tabs?

Answer 1

Problem was solved very simply. I had to set the HorizontalScrollBarVisibility="Auto". I checked http://msdn.microsoft.com/en-us/library/system.windows.controls.scrollviewer.horizontalscrollbarvisibility.aspx to see what the default value is for this property, but didn't see one there or on the ScrollViewer page. I assume it defaults to "Hidden".
Anyhow, once set to "Auto" the repeat buttons are shown only when the tabs overflow.