Installing 12.04 on a Fujitsu Primery TX100 S3 - Grub-install /dev/mapper error

[Paolo Sammicheli]

Installing 12.04 on a Fujitsu Primery TX100 S3 (with hardware RAID1).
Grub-install /dev/mapper error. It proposed me to select other devices but it failed in every one.
After few tries it ubiquity crashed and prompted to open a bug.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: ubiquity 2.10.20
ProcVersionSignature: Ubuntu 3.2.0-29.46-generic 3.2.24
Uname: Linux 3.2.0-29-generic x86_64
ApportVersion: 2.0.1-0ubuntu12
Architecture: amd64
CasperVersion: 1.315
Date: Sat Dec 1 12:16:54 2012
InstallCmdLine: noprompt cdrom-detect/try-usb=true file=/cdrom/preseed/ubuntu.seed boot=casper initrd=/casper/initrd.lz quiet splash -- debian-installer/language=it keyboard-configuration/layoutcode?=it maybe-ubiquity
LiveMediaBuild: Ubuntu 12.04 "Precise" - Build amd64 LIVE Binary 20120818-14:53
ProcEnviron:
 TERM=unknown
 PATH=(custom, no user)
 LANG=it_IT.UTF-8
 SHELL=/bin/bash
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)

[Paolo Sammicheli (xdatap1)]

Update: If in ubiquity I leave the default "/dev/mapper" in the GRUB drop-down box it doesn't works. If I select the first volume on the disk before the installation it works. The same option given after the error doesn't works. It looks like a UI bug.