[gentoo-embedded] Adding new users when using buildroot?

[Ed W]

Hi, I am building a small buildroot using say:

ROOT=/var/embedded/builds/base1 PORTAGE_CONFIGROOT=/var/embedded/portage 
emerge -v dropbear

The end result seems to be that I get my new user added to the build 
system, but not to the ROOT= system.  I have seen a few people report 
issues when using packages, but is this just a known limitation of 
recent portage or do I need some other commandline incantations?

Obviously plenty of other ways to solve this, but curious if there is a 
solution within the portage build process?

Thanks

Ed W