The doc and man page build commands respect '--build-base' passed to the 'build' command. The install commands don't. As a result, built docs end up in a directory that install_docs and install_man commands doesn't use. It should be pretty trivial to make install_* commands respect --build-base as well.
Moved to https://github.com/pkgcore/pkgcore/issues/83. Non-ebuild related pkgcore issues don't belong on bugzilla anymore.