Content inserted under the BODY element is sometimes ignored

{{velocity}}
{{html clean="false"}}
#set ($discard = $xwiki.ssfx.use('uicomponents/viewers/diff.css', true))
#set ($discard = $xwiki.jsfx.use('uicomponents/viewers/diff.js'))
#set ($old = '<div>one</div>')
#set ($new = '<div>one</div>
  <div>two</div>')
#set ($htmlDiff = $services.diff.html.unified($old, $new))
<div class="html-diff">
  #if ($htmlDiff == '')
    No changes.
  #elseif ("$!htmlDiff" == '')
    Failed to compute the changes.
  #else
    $htmlDiff
  #end
</div>
{{/html}}
{{/velocity}}