Comment # 4 on bug 1191728 from Josef Reidinger

(In reply to Joaqu���n Rivera from comment #3)
> As requested offline, in /etc/default/grub is present the value:
> GRUB_THEME=/themes/theme.txt
> 
> But that folder does not exist in the installed system.

And that is probably issue as we run grub in target system, so it cannot see
insts-sys content. Idea is that if you have installed multiple themes, you can
pick one, but not to modify it in insts-sys.