There may be cases in which FEATURES="preserve-libs" causes more harm than good, so it would be useful to give ebuilds the ability to explicitly disable it by setting RESTRICT="preserve-libs".
This is fixed in git: http://git.overlays.gentoo.org/gitweb/?p=proj/portage.git;a=commit;h=22b8c3bbe79a9fe23752375dadcf42b09c24b20c
This is fixed in 2.1.11.63 and 2.2.0_alpha174.