From: http://devmanual.gentoo.org/ebuild-writing/users-and-groups/index.html You may also use the pkg_preinst or pkg_setup functions for user creation, if the user is not required during src_compile. However, it appears that pkg_preinst runs after src_install. So, that sentence should probably be modified to indicate that pkg_preinst is only acceptable if the user/group is not required during or before src_install.
Created attachment 294991 [details, diff] Patch to implement my suggested change. Attached patch to fix issue.
I committed my change.