I'm not sure, if this is still a problem, but there's no code dealing with removal of symlinks in .../doc/$PF in the latest stable ebuild.
Created attachment 63657 [details] stale-xorg-docs output of `tree -p /usr/share/doc/xorg-x11-6.8.*`
It probably is. Care to provide a patch?
Well, lanius solved this by adding pkg_preinst() { # cleanups rm -fR /usr/share/doc/${PN}* } to cups and it's probably a good idea to clean out docs of previous versions as well. On the other hand putting [ -n "${PF}" ] && rm -fR /usr/share/doc/${PF} in pkg_postrm() would be a bit more safe. An accidentally empty $PN would not be funny in the first case.
better make that pkg_postrm(){ [ -n "${PF}" ] && rm -rf ${ROOT}/usr/share/doc/${PF} }
Security fixes only for the monolith now.