question on AttributeQuery processing

I was wondering what drove the rule in section 3.3.2.3 that requires
that an AttributeQuery containing an Attribute element containing an
AttributeValue must not be answered with a statement containing the
Attribute element with different AttributeValue element.

Examplified, should be that an AttributeQuery containing this

<Attribute Name="Department">
  <AttributeValue xsi:type="xs:string">aDepartment</AttributeValue>
</Attribute>

must not ne answered with an assertion containing

<Attribute Name="Department">
  <AttributeValue xsi:type="xs:string">aDepartment</AttributeValue>
  <AttributeValue
xsi:type="xs:string">anotherDepartment</AttributeValue>
</Attribute>

Am I misinterpreting something?
If not, can you clarify the meaning of that rule? It doesn't look to me
to strange a use pattern, to have a responder wanting to add other
values to those explicitly requested. Indeed is what my application need
to do.

Valerio