os-prober does not recognize other os on different hd

 /etc/grub.d/30_os-prober cannot detect the XP partition.

As the following info shows I have XP installed on sda while linux is on sdb

 fdisk -l /dev/sda
   Device Boot Start End Blocks Id System
/dev/sda1 * 63 134223074 67111506 7 HPFS/NTFS/exFAT

 fdisk -l /dev/sdb
   Device Boot Start End Blocks Id System
/dev/sdb1 63 59579107 29789522+ 7 HPFS/NTFS/exFAT
/dev/sdb2 59580414 240121727 90270657 5 Extended
/dev/sdb5 103462191 240121727 68329768+ 83 Linux
/dev/sdb6 59580416 101548031 20983808 83 Linux
/dev/sdb7 101550080 103458815 954368 82 Linux swap / Solaris

Partition table entries are not in disk order

The obvious workaround is to write an entry in 40_custom

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: grub-common 1.99-12ubuntu5
ProcVersionSignature: Ubuntu 3.0.0-15.26-generic 3.0.13
Uname: Linux 3.0.0-15-generic i686
ApportVersion: 1.23-0ubuntu4
Architecture: i386
Date: Sun Jan 29 10:24:20 2012
InstallationMedia: Ubuntu 10.04 LTS "Lucid Lynx" - Release i386 (20100429)
ProcEnviron:
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: grub2
UpgradeStatus: Upgraded to oneiric on 2011-11-05 (84 days ago)
mtime.conffile..etc.grub.d.40.custom: 2012-01-29T09:31:29.446168