>>>Whoa. That's just a cop-out. Why should you have to mess with the ControlTemplate to get that to work.
>>>If you run your code with NO style modifications to the TreeViewItem then the UI performs exactly as expected.
>>>Add in my basic style with the bindings and trigger. Again the UI is fine - and the bindings now also work as expected.
>>>But when the ControlTemplate is added to the Style then the bindings don't work. Given that the template is identical to the default why the >change in behaviour?
>>
>>No clue, but I've seen it before. Not all the binding will be hooked up correctly.
>>
>>I'll often pull my starting template from the ControlTemplateExamples in the Windows SDK just to avoid it. But the show me the template ones are nice because they are more complete. And if you are just trying to do a minor change that a big plus.
>
>If I can't solve this I might open a MS ticket.
>Do you mind if I use your code sample (it's simpler repro code than my actual code)
>Best,
>Viv

Go for it on my sample code.

I think what is happening is that in using reflection to get the template, some of the bindings are getting evaluated and returning their value instead of the binding. Hence:

IsChecked="{Binding Path=IsExpanded, RelativeSource={RelativeSource TemplatedParent}}"

becomes:

IsChecked="False"