When there is no media-libs/libpng:1.2 in the system I get this message on running emerge: !!! existing preserved libs: >>> package: media-libs/libpng-1.2.50 * - /usr/lib/libpng12.so.0 * used by /opt/dropbox/libwx_gtk2ud_adv-2.8.so.0 (net-misc/dropbox-1.2.48-r1) * used by /opt/dropbox/libwx_gtk2ud_core-2.8.so.0 (net-misc/dropbox-1.2.48-r1) * used by /opt/dropbox/libwx_gtk2ud_qa-2.8.so.0 (net-misc/dropbox-1.2.48-r1) There is dependency in media-libs/libpng:1.2 in the latest dropbox ebuild (net-misc/dropbox-1.6.16), it also should be added to the stable one.
or stablize a later version and punt the old one would be my vote.
@arches, please stabilize.
amd64 stable
x86 stable. Last arch, closing