[CentOS] installer and os-prober not finding Windows XP installation

I installed CentOS 7 on a Shuttle X27D box (dual-core Atom 330), and
so far it seems to work fine, but it didn't set up a Grub2 entry for
the existing Windows XP installation in the first partition (MBR).
Running os-prober generates no output.

fdisk shows that the NTFS partition is still present as /dev/sda1, and
still has the bootable flag set.

I added a menuentry for Windows to the end of /etc/grub.d/40_custom:

menuentry "Windows" {
set root=(hd0,1)
chainloader +1
}

and ran:

grub2-mkconfig >/boot/grub2/grub.cfg

and that lets me boot Windows, but I thought this was supposed to be
taken care of automatically.  Is there any known problem that prevents
the installer or Grub2 from finding Windows XP?

I don't normally set up dual-boot on production machines, but I use it
a lot for testing.

Thanks,
Eric