My guess is that our grub version is missing some features for recent EFI firmwares.

Unlike other distros we are still using the official grub-2.0 relase without any patches... I think other distros are using 2.02, which is in alpha state.

I'd try updating the grub pkg, building a live image with this grub pkg and testing the installation. You can achieve this easily with `xbps-src` and `void-mklive`:

    $ ./xbps-src pkg grub
    $ ./mklive.sh -r /path/to/your/local/host/binpkgs -r http://repo.voidlinux.eu/current ...