CREATE_HOME was inadvertantly set to 'yes' in Gentoo's stock login.defs. Changed it to 'no' as it is a RedHat'ism that the stock shadow package doesn't support. useradd from the stock shadow package generates a warning message which was a constant source of confused Gentoo users, if CREATE_HOME is set to 'yes'. Learned something new from that.
Got R and octave working for Gentoo and cleaned up some user contributed ebuilds.