DataBinding to RelativeSource Tag - wpf

Question

I am trying to use the Tag property as the source of a Binding, but the value is null when it gets to the converter.
What am I doing wrong?
Consumer
<Button Style="{StaticResource AddNewItemButtonStyle}" Tag="blah" />
Binding
<Style x:Key="AddNewItemButtonStyle" BasedOn="{StaticResource blueButtonStyle}"
TargetType="{x:Type Button}">
...
<AccessText Text="{Binding RelativeSource={RelativeSource Self},
Path=Tag, Converter={StaticResource AddNewItemForLabel}}">
</Style>
UPDATE
I added a setter for the ToolTip using the same strategy, and that does work BUT only after the second call to the converter (triggered by mousing over).
Can you see why the binding wouldn't work on the first pass?
Is there some place else besides the Tag that I can use more reliably?
2nd UPDATE
Based on Phil's input I changed my style to the xaml below. Must I add a Template property to the style?
<Style x:Key="AddNewItemButtonStyle" BasedOn="{StaticResource blueButtonStyle}" TargetType="{x:Type Button}">
<Setter Property="resx:ResxExtension.DefaultResxName" Value="Smack.Core.Presentation.Resources.MasterDetail"/>
<Setter Property="Content" >
<Setter.Value>
<StackPanel Orientation="Horizontal">
<Image Source="{resx:Resx ResxName=Smack.Core.Presentation.Resources.MasterDetail, Key=bullet_add}" Stretch="Uniform" />
<AccessText VerticalAlignment="Center" Text="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=Tag, Converter={StaticResource AddNewItemForLabel}}" />
<ContentPresenter/>
</StackPanel>
</Setter.Value>
</Setter>
<Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=Tag, Converter={StaticResource AddNewItemForToolTip}}"/>
<Setter Property="Command" Value="{Binding AddNewItemCommand}" />
</Style>

Answer 1

If you change the xaml in the answer I gave to your other question to
<AccessText Grid.Column="1" VerticalAlignment="Center">
<AccessText.Text>
<MultiBinding StringFormat="{}_{0} {1}">
<Binding Source="{StaticResource Test}"/>
<Binding RelativeSource="{RelativeSource TemplatedParent}" Path="Tag"/>
</MultiBinding>
</AccessText.Text>
</AccessText>
Then Tag will work.
Or you can use the short form of TemplateBinding
<AccessText Grid.Column="1" VerticalAlignment="Center" Text="{TemplateBinding Tag}"/>
or the long form
<AccessText Grid.Column="1" VerticalAlignment="Center"
Text="{Binding RelativeSource={RelativeSource Mode=TemplatedParent}, Path=Tag}"/>
or, your style will work like this (bits deleted for testing):
<Style x:Key="AddNewItemButtonStyle" TargetType="{x:Type Button}">
<Setter Property="Content" >
<Setter.Value>
<StackPanel Orientation="Horizontal">
<AccessText VerticalAlignment="Center"
Text="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Button}}, Path=Tag}" />
<ContentPresenter/>
</StackPanel>
</Setter.Value>
</Setter>
<Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Mode=Self}, Path=Tag}"/>
</Style>