xsl-region-body errors from fop when double.sided=1

Hi,

I've been trying to build a PDF with the parameter double.sided set to 1, but
when I do so, fop barfs with the following error:

java.lang.IllegalStateException: Flow 'xsl-region-body' does not map to the regi
on-body in page-master 'blank'.  FOP presently does not support this.

I'm using the docbook-xsl-1.69.1 (I didn't have this problem with 1.68).

I tried setting fop.extension to 1 but this simply produced another error.

Can anyone help? I hope so, I really need double.sided :)

Matt