Trouble with simple fo:list-block

I am trying to use the fo:list-block object with a variable length
list-item-label with the expectation that the list-item-body will format
beside the list-item-label. Because the list-item-label will be of
varying lengths I'm not specifying a
provisional-distance-between-starts.

If I format the following, the YYYYYYYYYYYYY text formats over the xxxxx
text. I have tried adding attribute start-indent="body-start()" to
list-item-body and the result is a fixed distance between starts and a
similar overset. This seems really simple - am I missing something or
might there be an inheritance I need to look out for?

I am formatting with Antenna House formatter V5.2

<fo:list-block>
  <fo:list-item>
    <fo:list-item-label>
      <fo:block>
	<xsl:text>xxxxx</xsl:text>
      </fo:block>
    </fo:list-item-label>
    <fo:list-item-body>
      <fo:block>
	<xsl:text>YYYYYYYYYYYYY</xsl:text>
      </fo:block>
    </fo:list-item-body>
  </fo:list-item>
</fo:list-block>