c14n Inclusive question.

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I'm rewriting the inclusive canonicalization and i see same weirds thing 
in the test vector:

/data/interop/c14n/Y4/c14n-1.txt:

<bar:Something xmlns:bar="http://example.org/bar"; xml:lang="en-ie">
    <foo:Something xmlns:foo="http://example.org/foo";>
       <bar:Something xmlns:bar="http://example.org/bar";>
          <foo:Something xmlns:foo="http://example.org/foo";>
            <baz:Something xmlns:baz="http://example.org/baz";></baz:Something>
          </foo:Something>
       </bar:Something>
    </foo:Something>
 </bar:Something>


Is valid and this one not:

<bar:Something xmlns:bar="http://example.org/bar"; xml:lang="en-ie">
    <foo:Something xmlns:foo="http://example.org/foo";>
       <bar:Something>
          <foo:Something>
            <baz:Something xmlns:baz="http://example.org/baz";></baz:Something>
          </foo:Something>
       </bar:Something>
    </foo:Something>
 </bar:Something>
Why is needed to redeclare the xmlns:foo & xmlns:bar in the same prefixes?
I have readed the spec and doesn't see why, I'm getting mad about it.
Thanks in advance.