Keying over added attributes in temporary tree

"A key can be used to select nodes in any document, not just the
principle document. This includes a document constructed as a
temporary tree." - Kay XSLT2.0 3ed, pg 334

I am trying to create a key of the elements in a temporary tree. This
temporary tree is the result of a "first phase" processing that adds a
new attribute to the element.

I would assume that the keys are created before starting the "/" template.
The xsl:key element is not allowed in a template, so that can't force
the re-indexing for the key.

Two questions:
1) Is the xsl:variable "objects-with-new" considered a "temporary tree"?
2) Is it possible to access the "object" elements in $objects-with-new
via a key, where the @use is an attribute that was added after parsing
the input document?

Regards,
Tim Lebo

Input:
<?xml version="1.0" encoding="UTF-8"?>
<root>
  <object id="a">
  </object>
  <object id="b">
  </object>
  <object id="c">
  </object>
</root>

XSLT 2.0 (saxon8b):
      1 <?xml version="1.0"?>
      2 <xsl:transform
xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="2.0">
      3 <xsl:output method="xml" indent="yes"/>
      4
      5 <xsl:key name="objects-by-id"  match="object" use="@id"/>
      6 <xsl:key name="objects-by-new" match="object" use="@new"/>
      7
      8 <xsl:template match="/">
      9   <xsl:comment>Successful attempt to access input nodes by
key</xsl:comment>
     10   <xsl:copy-of select="key('objects-by-id','b')"/>
     11
     12   <xsl:variable name="objects-with-new">
     13     <xsl:apply-templates select="//object" mode="addnew"/>
     14   </xsl:variable>
     15
     16   <xsl:comment>Objects with added attribute</xsl:comment>
     17   <xsl:copy-of select="$objects-with-new"/>
     18
     19   <xsl:comment>Successful attempt to access by more expensive
xpath expression</xsl:comment>
     20   <xsl:copy-of select="$objects-with-new//object[@new=2]"/>
     21
     22   <xsl:comment>Failed attempt to access keyed by new
attribute</xsl:comment>
     23   <xsl:copy-of select="key('objects-by-new','2')"/>
     24 </xsl:template>
     25
     26 <xsl:template match="object" mode="addnew">
     27   <xsl:copy>
     28     <xsl:copy-of select="@*"/>
     29     <xsl:attribute name="new">
     30       <xsl:number/>
     31     </xsl:attribute>
     32     <xsl:apply-templates/>
     33   </xsl:copy>
     34 </xsl:template>
     35
     36 </xsl:transform>


Output:
<?xml version="1.0" encoding="UTF-8"?>

<!--Successful attempt to access input nodes by key-->
<object id="b"></object>

<!--Objects with added attribute-->
<object id="a" new="1"></object>
<object id="b" new="2"></object>
<object id="c" new="3"> </object>

<!--Successful attempt to access by more expensive xpath expression-->
<object id="b" new="2"></object>

<!--Failed attempt to access keyed by new attribute-->
THERE IS NO ELEMENT HERE, BUT "<object id="b" new="2"></object>" IS DESIRED