Included dt file not override-able by inherited template

[rjframe]

I have the following file setup, using diet-ng with vibe.d (WebInterface)(the original diet implementation also has this issue):

layout.dt provides my page structure.
leftnav.dt is included by layout.dt for navigation.
And my pages, which extend layout.dt and attempt to override a block in leftnav.dt. I would expect that since the block is included by layout.dt any file that extends layout.dt would be able to override it, but my attempts to do so are ignored - the overriding block doesn't make it into the html at all.

If I actually copy the contents of leftnav.dt into layout.dt everything works as expected. According to the diet documentation include is effectively a copy-paste, but it isn't quite working that way.

I could also work around it by passing data to the render function (as adding "active" to the li class is all I really care about here), but would prefer not to do that.

//- layout.dt
doctype html
html(lang="en")
	head
		block head
			title Diet Include Test
	body
		div
			//- I'll want to modify blocks in leftnav in child templates.
			include leftnav
		div.main
		block content
				p Content goes here.

//- leftnav.dt
ul
	//- These blocks should (but don't) let me adjust each individual item in other templates.
	block navIndex
		li
			a(href="/") Home
	block navPage2
		li
			a(href="/pagetwo") Not Home

//- index.dt
extends layout
//- I expect this block to override the block in layout.dt via the include, but is ignored.
block navIndex
	li
		a(class="active", href="/") Home Override
block content
	h1 Hello!
	p "Home" should say "Home Override".

//- pagetwo.dt is much the same as index
extends layout
block head
	title Diet Test - Page Two
block navPage2
	li
		a(class="active", href="/pagetwo") Page Two
block content
	h1 The second page.
	p "Not Home" should say "Page Two".