The ebuild has this: src_unpack() { cp "${DISTDIR}"/* "${S}" } Now the package manager may use the real DISTDIR, or it may use a "shadow" dir instead. The ebuild must not rely on either of these cases. If DISTDIR is the real dir, ${S} will end up with a lot of files.
Fixed in 2ea322cc35bb2d4926bd6637af82e796622bfdd7.