sean@lois sean $ cat /usr/portage/dev-util/gperf/gperf-2.7.2.ebuild ... RDEPEND="virtual/libc >=sys-apps/sed" ... ">=sys-apps/sed" is not a valid depatom. Should be just "sys-apps/sed".
>=sys-apps/sed-4 actual, but yes, a bug. Fixed in CVS. Thanks for the bug report.