There is a bug in the SDK:
xmlDomInstance:name() is supposed to return both the name and namespace of element nodes. it does return the namespace of the root node, but for all other nodes it returns nil for the namespace. For example, when reading an xmp file, in which case all elements have namespaces.
Can you tell me if this is on Mac or Windows? The code behind the XML parser API is quite different between platforms.
Windows 7 / 64-bit.