The current code of portage returns an error during info directory index regeneration if there are directories in /usr/share/info (I was going to create /usr/share/info/emacs-21.3 and /usr/share/info/emacs-21.3.50 to support multiple versions of emacs). I'll attach a patch to skip directories found in ${INFOPATH}.
Created attachment 36636 [details, diff] emerge-infopath.diff
Added the patch to cvs. Thanks
patch was released in pre18.