Page breaks for programlisting elements

Using FOP 1.0. Docbook XML -> FO -> PDF.

Some of the page breaks for my  programlistings look bad. They leave a
single orphan line at the bottom of the page. So the grey background box splits over 2 pages.

 I have tried the following FO processing instructions for the relevant
blocks, but they have no effect.

<?dbfo keep-together="always" ?>  (is this only for formal objects --
 tables, figures etc?)

 <?dbfo-need height="2in" ?> (this does not "push" the following block on to
 the next page, as expected)