guix configuration problem : bootloader "menu-entry"

[Fulbert]

Hello Guixers !

I am adding some `menu-entries` to my bootloader-configuration.

>From `$ info "(guix)Bootloader Configuration"`
     ‘device’ (default: ‘#f’)
          The device where the kernel and initrd are to be found—i.e.,
          for GRUB, “root” for this menu entry (*note (grub)root::).

          This may be a file system label (a string), a file system UUID
          (a bytevector, *note File Systems::), or ‘#f’, in which case
          the bootloader will search the device containing the file
          specified by the ‘linux’ field (*note (grub)search::).  It
          must _not_ be an OS device name such as ‘/dev/sda1’.

My problem is that `device` (or no device at all) does not seem to
work as expected. Whatever the `device`, guix produces an identical
`search --file…` grub menuentry.

Attached are 3 configuration test entries and their resulting
`menuentry` in grub.cfg. Not sure how to produce a "bytevector"
for the UUID though, but at least the test with a label (literal
string) should produce something like :

  "search --label --set debian-stable"

Correct ? Or do I miss something ?!

Thanks for you time !

configuration.scm.extract
Description: Text document

grub.cfg.extract
Description: Text document