SP Attribute Extractor multiple values when using NameID and Attribute

[Peter Schober]

* Aaron Howell <aaron.howell at deakin.edu.au> [2017-04-05 07:21]:
> I’ve made the change in dev so now the SAML Assertion contains an
> attribute with a Name and a NameID with a Format for the same URI -
> using the URI for NameID is recommended and can’t filter the
> attribute before Generation. However it seems the SP extracts the
> two values and populates the one variable as multivalued with both
> values the same. I can’t seem to work out a way to stop this
> behaviour.
> 
> So the assertion contains:
> <saml2:NameID xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion" Format="urn:oid:XXXXXXX" NameQualifier="https://idp.example.com/idp/shibboleth" SPNameQualifier="https://sp.example.com/shibboleth”>value</saml2:NameID>
> <saml2:Attribute FriendlyName=“XXXXXXX" Name="urn:oid:XXXXXXX" NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:uri">
>       <saml2:AttributeValue>value</saml2:AttributeValue>
>     </saml2:Attribute>

So you're sending the same information twice to the same SP, once as
an Attribute (within the AttributeStatement) and again as a NameID
(within the Assertion/Subject)?
May I ask why?
-peter