nested functions issue

[wolfsoft]

When a function calls another function, the parsing error occurs:

<?xml version="1.0"?>

<dbp:module
	xmlns:dbp="http://dbpager.org.ru/schemas/dbp/3.0"
	xmlns:lib="http://dbpager.org.ru/schemas/dbp/3.0/custom/lib"
	xmlns:app="http://dbpager.org.ru/schemas/dbp/3.0/custom/app"
	xmlns="http://www.w3.org/1999/xhtml"
>

<dbp:var name="test" value="TEST">
	{lower(upper($test))}
</dbp:var>

</dbp:module>

Expected result:

test

Actual result:

Fatal error: invalid expression: ")" expected