With commit 7290a72e3c xbmc will correctly check the distro release files now when lsb_release does not exist. This means that the ebuild no longer needs to "avoid" the lsb_release dependency and the relevant sed line can now be removed.
should be all set now in the tree; thanks for the report! Commit message: Drop lsb_release hack now that upsream is good http://sources.gentoo.org/media-tv/xbmc/xbmc-9999.ebuild?r1=1.110&r2=1.111