Nested [insert_tag] calls do not work

[CelticMinstrel]

It would be natural to expect you can nest [insert_tag] calls in a similar way to how you can nest $ substitutions, but it does not work.

Example (in Lua for simplicity):

wml.array_access.set('madness', { {name = 'object', variable = 'object'}, {name = 'trait', variable = 'trait'}})
wml.array_access.set('object', {{id = 'one'},{id = 'two'}})
wml.array_access.set('trait', {{id='foo'},{id='bar'}})
print(wml.tostring(wml.tovconfig{wml.tag.insert_tag{name='insert_tag', variable='madness'}}))

This results in the following WML being printed to the console:

[insert_tag]
	name="object"
	variable="object"
[/insert_tag]
[insert_tag]
	name="trait"
	variable="trait"
[/insert_tag]

I would expect to instead see the following WML:

[object]
	id="one"
[/object]
[object]
	id="two"
[/object]
[trait]
	id="foo"
[/trait]
[trait]
	id="bar"
[/trait]

Note: This is definitely not a good first issue, as substitution of these tags is handled in two or three parallel places.