Umlaut in an iso-8859-1 encoded base file

A very special error situation.
I have a base file in the scheduler.xml. In the iso-8859-1 encoded base file I have a comment with an UMLAUT.

<?xml version="1.0" encoding="iso-8859-1"?>

<spooler>
    <config>	
	<commands>
            <add_order id="test" replace="yes" job_chain="/test/job_chain1">
        	<params>
        	    <param name="foo" value="bar"/>
                    <!-- here a comment with special chars äöüß -->
        	</params>
            </add_order>
        </commands>		
    </config>
</spooler>

Then the JobScheduler logs the following error and will be terminated. See attached log. The place of the comment is significant. If I move the comment outside the add_order then no error occurres.

.

Unknown macro: {scheduler}

[ERROR] Z-JAVA-105 Java exception com.sos.scheduler.engine.common.xml.XmlUtils$XmlException("net.sf.saxon.trans.XPathException: Character in comment cannot be represented in the selected encoding (code 228)