It seems that the docbook parser cannot find the required dtd's to compile koffice at all. The same behaviour can be seen with the vanilla koffice-1.2 source package directly from ftp.kde.org. The failure happens in /koffice-1.2/doc/kugar/index.docbook parsing.
this is probably the same as http://bugs.gentoo.org/show_bug.cgi?id=10767 emerge libxslt-1.0.20 libxml2-2.0.24 kdelibs and then emerge koffice should work
>=libxml2-2.4.28 is also good. Status?
The suggested downgrading of libxml2 and libxslt to libxslt-1.0.20 / libxml2- 2.0.24 and re-emerging kdelibs and then koffice did work. I haven't tried upgrading libxml2 to 2.0.28 as suggested in a latter advisory. Thank you for your assistance.