Let me reply to myself, I found the culprit.
In com.sun.xml.rpc.streaming.XMLReaderUtil.decodeQName(XMLReader
reader, String rawName) the source code actually states what is my
problem:
// NOTE: Here it is assumed that we do not want to use default namespace
// declarations and therefore a null prefix means "no namespace" and
// not "default namespace"
There it is, no prefix means no namespace, not the default namespace.
On the other hand .Net in this context means no prefix means the
default namespace. I may or may not do additional research as to which
interpretation is correct in this particular case. Any additional
comments should be, imo, handled in the developers list.
Jerry Pisk