After emerging portage 2.0.28, all packages are reported as [masked]. The bug appears both during bootstrap and on finished installation. Workaround: changing the requirements in /etc/make.profile/packages to =2.0.13 rather than the default (>=1.8.x). I have also tested manually emerging 2.0.29 with identical result. 2.0.13 and 2.0.11 both works fine.
this is not a bug but what portage does with keywords. As most keywords have been added for sparc, I'm closing this bug.