Question to cutomization of docbook-xsl

Hi there,

can anyone explain me how to prevent the empty page after the preface in the
docbook-xsl styles for FO?

I have no problem to do this with recto/verso - pages in a <book>, but I
didn't find a solution for <preface> (and the funny thing is: if I skip the
chapters after the preface so that just the auto-glossary follows, the empty
page is gone)

Many thanks in advance,
Thomas