EqualToXml does not detect difference on certain XML documents if Xalan is on classpath

[thake]

Proposal

The EqualToXml matcher does not detect differences on certain XML documents if Xalan is on the classpath.
The documents need to use the same namespace URI twice with a different namespace prefix. Example:

<?xml version='1.0' encoding='UTF-8'?>
<S:Envelope xmlns:S="http://schemas.xmlsoap.org/soap/envelope/" xmlns:SOAP="http://schemas.xmlsoap.org/soap/envelope/">
   expected
</S:Envelope>

Xalan itself does not seem to be the problem because one can use XmlUnit to correctly detect differences in such XML documents.

Reproduction steps

I've created a demo project with Unit tests that demonstrate the bug and the different behavior of XmlUnit and EqualToXml: https://github.com/thake/wiremock-bug/blob/main/src/test/java/com/example/XmlUnitTest.java

References

No response

[thake]

The error disappears if SkipResolvingEntitiesDocumentBuilderFactory.newDocumentBuilder() no longer returns a cached DocumentBuilder but a fresh one.