mail-client/sylpheed-3.5.1 has automagic on dev-libs/dbus-glib-0.102,net-libs/liblockfile-1.09
https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=511501b1893437d0f2cf30d98ee77d8b17f70fa5 Thank you for reporting! Fixed in 3.6.0.