generating an index with 2 columns

Hello,

I am generating a pdf version of my docbook document using 
docbook-xsl-1.71.1 and XEP-4.7. In the resulting output, the Index page 
has one column only. I am using the default titlepage.templates.xsl. 
Although the default value for column.count.index is 2, I tried setting 
this parameter explicitly to 2 and then 3 with no changes. There is 
always one column only. What am I doing wrong?

Diane Larin
INRO