I tried FOP 0.20.1 (on the commandline) and found that the bookmark extension (fox:outline, fox:label) does not work (in FOP 0.18.1 it did). Running FOP 0.20.1, there is no error reported but opening the PDF-File in AcrobatReader 5.0, the bookmark column is empty.
FWIW, I found the same (that it didn't work with the FOP 0.20.1 release build, but that it did work after building FOP from xml-fop_20010927161603.tar.gz. As a learning exercise, I may try to spent a bit of time figuring out what the difference is.
This was broken due to the stream renderer changes. It works in 0.20.2
batch transition pre-FOP1.0 resolved+fixed bugs to closed+fixed