Pub.schema:validate using document type

[DevNull43]

I think you must inspect the conformsTo value you are setting, this value affects the result:

conformsTo: String Document type or schema to validate object against.

       - If object is a document (Data object), conformsTo must specify the 
            fully qualified name of a document type on the Integration Server.
       - If object is a com.wm.lang.xml.Document or 
            com.wm.lang.xml.Node object, conformsTo must specify the fully 
            qualified name of an IS schema on the Integration Server.
       The specified IS schema is needed only for validating nodes with 
       “Names” that are not from XML Namespaces (that is, qualified nodes 
       whose XML Namespace Name properties are absent). Integration 
       Server can only locate the IS schema if its fully qualified name is 
       provided.
       If the XML document (com.wm.lang.xml.Document or 
       com.wm.lang.xml.Node) contains namespace‐qualified tags, 
       conformsTo is ignored. Instead, Integration Server uses the XML 
       namespaces declared in the instance document to locate the IS 
       schemas that contain definitions and declarations for that XML 
       namespace.

Hope this give you a hint