invalid within XML-Spy, .NET and Xerces parsers but valid with the W3C validator

Hi,

With the attached XML-Schema, a simplified version of one of our schema's,
we had some problems within XML-Spy.
The schema contains a content-model, which is judged by XML-Spy as invalid.
I know how to solve this invalidness, but that solution conflicts with the
desired model.

I wasn''t able to get a grip on the real source of this 'invalid' message by
XML-Spy.
Why is it invalid to have a minOccurs of 1 on the sequence element? So I
decided to try another validator, it might give me more clues.
I tried '*http://www.w3.org/2001/03/webdata/xsv*<http://www.w3.org/2001/03/webdata/xsv>
' enad surprisingly the schema was judged here as valid.

I concluded XML-Spy would probably have a bug because I put more trust in a
W3C validator.

So I sent a bug-report to Altova. A moment ago they answered me. They did
test the schema also on a .Net and the Xerces paser and also those parsers
reported an error.
Does this mean the W3C validator has a bug? If so, can you answer the
question above. The XML-Schema recommendation doesn't help me much.

I attached the mentioned schema.

Greetings,

Robert Melskens

*Atos Origin Nederland B.V.*