Comment 16 for bug 571893

As from this thread in the german ubuntu forum:
http://forum.ubuntuusers.de/topic/windows-7-bootet-nach-ubuntu-update-nicht/
there is evidence that this is not really a bug from grub but from the way the installer performs the upgrade.

If Grub2 is already installed on your system:
 * keep the current version of grub rather than choose the maintainer's version.
 * if you manually install Grub take care not to install grub to the Windows partition. In that case Windows will fail to start.