[oXygen-user] Abstract elements and substitution groups

Years ago, I set up a collection of schemas that use abstract elements and substitution groups to allow different models for certain elements. I just noticed that instance documents that use these schemas have always validated with the default processor (Xerces), and they appear to validate with MSXML 4.0, they don't validate with Saxon-EE or MSXML.NET. XML is a small part of what I do, so I'm not confident that my interpretation of the spec is correct. I've attached a test case that replicates the behavior I'm seeing in a minimal package. I'd appreciate it if someone could look it over and tell me who's right. I think the documents explain themselves, but I'm happy to provide more information about anything that's not clear.