subscript with fop

Hi,

I use some subscripts in my Master's thesis, written in Docbook. When I 
use the DocBook XSL stylesheet, version 1.65.1, with FOP 0.20.5, the 
subscript aren't "subscripted". They just get a smaller font, but their 
baseline doesn't change. Is this a limitation of FOP or can I 
circumvent this problem in any way?

Thanks in advance,

Koen Vervloesem
--
"Efficiency is intelligent laziness."