games-strategy/ufo2000 ~x86(package keywords, same story with ~amd64 keyword) =games-strategy/ufo2000-0.6.627(package.unmask file) games-strategy/ufo2000 emerge ufo2000 Calculating dependencies !!! All ebuilds that could satisfy "ufo2000" have been masked. !!! One of the following masked packages is required to complete your request: - games-strategy/ufo2000-0.6.627 (masked by: missing keyword)
See http://gentoo-wiki.com/TIP_Dealing_with_masked_packages
Not a bug.