Constructing a Map Using xsl:for-each-group

I want to construct a map where the keys are attribute values and the entries contain the elements that exhibit those attribute values. The obvious way to do this is with for-each-group:

      <xsl:variable name="links-by-target-id" as="map(xs:string, element()*)">
        <xsl:map>
          <xsl:for-each-group select="$docbook-links" group-by="@linkend">
            <map:entry key="{current-grouping-key()}">
              <xsl:sequence select="current-group()"/>
            </map:entry>
          </xsl:for-each-group>
        </xsl:map>
      </xsl:variable>

However, using Saxon 9.8.0.8 from Oxygen I get this message:

"Required item type of xsl:map sequence constructor is map(*); supplied value (xsl:for-each-group) has item type element(). The expression can succeed only if the supplied value is an empty sequence."

The XSLT spec says that the contents of <xsl:map> is a sequence constructor, which for-each-group certainly is.

Is this message legit? I don't see how it can be but maybe I'm missing a subtlety in the map instruction?

Thanks,

Eliot
--
Eliot Kimber
http://contrext.com