When the emerge --autounmask-continue option is specified on the command line, it will not work if EMERGE_DEFAULT_OPTS contains --autounmask=n. This can be confusing, since it simply fails to work and emerge does not emit any messages to indicate that the options conflict with each other.
Patch sent for review: https://archives.gentoo.org/gentoo-portage-dev/message/4b959d8c508791d41683d61ccc1127ef https://github.com/gentoo/portage/pull/167
Updated patch to just show a warning, so that --autounmask=n remains effective: https://archives.gentoo.org/gentoo-portage-dev/message/c37dd18262de25a5fb46186f2050885a
This is in the master branch: https://gitweb.gentoo.org/proj/portage.git/commit/?id=565ceb1bebc83ec1a5572a672e2e08ea7d91e7a8