David:
I tried your version of envelope.xsd (which is simply a redirector) and it
worked for me.
What I did was to make a local copy of your envelope.xsd, modify a local
copy of msg-header-2_0.xsd to import from the SOAP Envelope namespace using
the locally cached copy of envelope.xsd (the redirector), and then open up
msg-header-2_0.xsd using XML Authority. No error was reported.
But the fundamental disagreement between you and Doug (or Chris) is that you
want to leave msg-header-2_0.xsd unchanged (still using the TC web site as
the imported schema location) whereas Doug and Chris (and I concur with
them) that the imported schema location should be the same as the SOAP
Envelope namespace URI.
I support Doug's suggestions for changes, provided the implementers are OK
with updating their software to import the official schema for the SOAP
Envelope namespace.
-Arvola