Can't generate nillable attribute from/to xml schema

I have a little problem - instant reverse/generator doesn’t see nillable, form and block attributes when I try to generate XML schema from object diagram. What’s wrong with that? Is it a property of VPforUML or I’ve done something wrong?

The Instant Generator and Instant Reverse are only take care about the class models, it will not consider about the object models during its operation. Please make sure you have modeled the attributes in class models.

Best regards,
Rain Wong