Hello,
The TabbedMdiHost.MaxTabExtent property does allow the tab to grow to larger size, but we also should have mentioned that there is a special TitleConverter value converter in place on the binding for the TextBlock that will only allow up to a certain number of characters to show. If the number of characters exceeds specifications, ellipses will be inserted in the middle of the text. That's what's happening here. We had to use a custom value converter since TextBlock can't do character ellipses in the middle of the text (like we generally want in this scenario). TextBlock only supports character ellipses at the end.
If you use this code for your TabbedMdiHost, it will work how you want since this TextBlock.Text binding doesn't use our value converter:
<docking:TabbedMdiHost MaxTabExtent="100000">
<docking:TabbedMdiHost.TabItemContainerStyle>
<Style TargetType="docking:AdvancedTabItem">
<Setter Property="Header" Value="{Binding TabTextResolved}" />
<Setter Property="HeaderTemplate">
<Setter.Value>
<DataTemplate>
<TextBlock Text="{Binding}" TextTrimming="CharacterEllipsis" TextWrapping="NoWrap" VerticalAlignment="Center" />
</DataTemplate>
</Setter.Value>
</Setter>
</Style>
</docking:TabbedMdiHost.TabItemContainerStyle>
...