Invalid encoding with umlauts and -xml -o

I try to run a test with "-xml -o result.xml" on Windows.
This test outputs a message with qDebug(), which contains umlaut characters.
The resulting xml file says 'encoding="UTF-8"', but the message is encoded in Latin1.

This violates the XML specification (http://www.w3.org/TR/REC-xml/#sec-cdata-sect) and causes the parser which should process this file to throw an exception:
com.sun.org.apache.xerces.internal.impl.io.MalformedByteSequenceException: Invalid byte 2 of 2-byte UTF-8 sequence.

On Linux, everything works fine.