The developer docs say: src_unpack: Use this function to unpack your sources and apply patches, and run autoconf/automake/etc. if necessary. By default, unpacks the packages in ${A} and applies ${PF}-gentoo.diff. The default starting directory is ${WORKDIR}. However, src_unpack just seems to unpack sources: it doesn't apply the *-gentoo.diff patch automatically. Are the docs old or is this something intended that hasn't been implemented yet?
According to /usr/lib/portage/bin/ebuild.sh, it is true that src_unpack() does not do any auto-patching.
Sunflare: can you fix this in our docs? It should not say that Portage auto-patches.
Fix submitted to peitolm and meekrob. I'll close this bug as soon as it gets through to the pages.
Assigning to me for the time being.
The webpage has been updated. Thanks for the heads-up, and thanks to peitolm for doing the update! Closing bug as FIXED.