'guix system build sys.scm' hangs (please see build1.txt)

I'm running on guixSD using guix built from git checkout ...

: guix (GNU Guix) 0.12.0
: Copyright (C) 2017 the Guix authors
: License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
: This is free software: you are free to change and redistribute it.
: There is NO WARRANTY, to the extent permitted by law.
:   File: /root/.config/guix/latest -> ../../../home/g1/src/guix
: v0.12.0-2730-gfc5b12879
: fc5b12879 gnu: diamond: Update to 0.8.37.
: * (HEAD detached at origin/master)        fc5b12879 gnu: diamond:
Update to 0.8.37.

... with a small edit to grub.scm (please see grub.diff)