The files rdoc-2 and ri-2 end up in / while they almost certainly belong into /usr/bin. If I read the docs in the ruby-fakegems.eclass right then second argument to ruby_fakegem_binwrapper should be a fully qualified path and prefixing /usr/bin/ in the ebuild did indeed fix the problem for me.
whoops, yes.
and fixed in -r1, thanks.