We believe that your issue has been closed by the upload of
Version 1.2.5 of grml2hd from Ulrich Dangel <mru@grml.org>.
The explanation is attached below

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Hash: SHA1

Format: 1.8
Date: Mon, 19 Oct 2009 23:55:57 +0200
Source: grml2hd
Binary: grml2hd
Architecture: source all
Version: 1.2.5
Distribution: unstable
Urgency: low
Maintainer: Michael Prokop <mika@grml.org>
Changed-By: Ulrich Dangel <mru@grml.org>
Description: 
 grml2hd    - make a harddisk installation of grml
Changes: 
 grml2hd (1.2.5) unstable; urgency=low
 .
   * Fix grub support in non-interactive mode.
     [Closes: issue707]
Checksums-Sha1: 
 43c9d48c8a2f2e2ee4049df79c05723cf2d7ba21 912 grml2hd_1.2.5.dsc
 1d1136a17ff3409dfb4c428c75dc9a86db41e5b1 294883 grml2hd_1.2.5.tar.gz
 e223a02725e9939e83f279086f0580fb3c705377 295528 grml2hd_1.2.5_all.deb
Checksums-Sha256: 
 8a0d6335a4853c91a53ef702ee0d352af90489e4c1528303be23000c395cbb66 912 grml2hd_1.2.5.dsc
 d4708efa9d9f54863ea2cf5cdafe8959a9da4808b449fbf4748bdafbcb9dcc09 294883 grml2hd_1.2.5.tar.gz
 b4671105819bdd5d49446e2e91f59eb20a1c76eb07341bd0f174415716f574b5 295528 grml2hd_1.2.5_all.deb
Files: 
 610d9620ebf6934ddba18f0ff37c5d41 912 grml optional grml2hd_1.2.5.dsc
 998293ded904ffc7799a400f4ac88fa7 294883 grml optional grml2hd_1.2.5.tar.gz
 7a9f0a220e4566a322560dec75319019 295528 grml optional grml2hd_1.2.5_all.deb

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Bugreport by al Sten-Clanton:

interactive + lilo + ext3: works
interactive + grub + ext3: works
non-interactive + lilo + ext4: works
non-interactive + grub + ext4: does not work
non-interactive + grub + ext3: does not work

Note by mika: ext4 is not yet supported, though it's on my todo-/wishlist. Why 
installation of grub fails in non-interactive mode has to be debugged.