The various DocBook DTDs set a NAMELEN constant that is too short for many
purposes, e.g. the GTK+ documentation. Is "44" now, should be more like 128
or 256 I think.
If you grep NAMELEN `find /usr/share/sgml -name "*"` and change all "44" to
something larger it will fix the problem. I haven't noticed any negative
side effects from doing this on my system.
Fixed in docbook-dtds-1.0-27.