>>FWIW the answer to this is pretty mundane.
>>I had a default Border style set in the app and the ControlTemplate for the TreeViewItem wraps the ToggleButton in two Borders....
>>
>>>In my TreeView the 'Expander' ToggleButton is getting chopped to about half of the height required to display it completely - and I don't understand why.
>>>
>>>If I drill in using Snoop I can see that it's Height is in fact hard coded at 13 but nothing (AFAICS) is constraining the height of the containing TreeViewItem - so why is it getting chopped?
>>>
>>>TIA,
>>>Viv
>
>I don't know how many times I've wanted a where the heck did that setting come from button in WPF.

I don't know how Snoop hooks in to the App but, oddly, it too was picking up the Style in its own TreeView - that should have given me a clue :-{