The multistatus response from a PROPPATCH request has the following start 
element:

<d:multistatus xmlns:d="DAV">

I believe it should be:

<d:multistatus xmlns:d="DAV:">

I perused the code and based on a quick glance it seems that
jakarta-
slide/src/webdav/server/org/apache/slide/webdav/method/PropPatchMethod.java is 
the cause.  Specifically:

        generatedXML.writeElement("d", "DAV", "multistatus",
                                  XMLPrinter.OPENING);

which I think should be:

        generatedXML.writeElement("d", "DAV:", "multistatus",
                                  XMLPrinter.OPENING);

Thanks,
Joe