Comment 5 for bug 772470

In that case, this is correct behaviour from os-prober. It's supposed to return the thing you can boot. In this case, the Windows boot loader is on sda2, so it returned that.

Ubiquity is going to need to change to track down the actual Windows root filesystem associated with a boot partition (somewhat like the way linux-boot-prober tracks down more information for Linux boot partitions). However, I'm going to bump this to P-series, as I think this is going to be too invasive for Oneiric, although I realise it's a problem.