There is problem in evaluation of expression in case that property for evaluation is defined after the expression.
In case of using DMR the order of property and expression definition is not taken in consideration and substitution works fine.

When you define system properties in xml like:

    <system-properties>
        <property name="qa.test.property" value="${qa.test.exp:defaultValue}"/>
        <property name="qa.test.exp" value="expression.value"/>
    </system-properties>

you start the container and then you can check the expression evaluation in jboss-cli.sh with command:

:resolve-expression(expression="${qa.test.property}")

The expression will be evaluated as "defaultValue" what is not correct because the "qa.test.exp" is defined.
When you switch definitions of properties (switch <property> tags) then the expression will be evaluated correctly (as "expression.value).