Comment 86 for bug 1265192

I suspect that auto-partitioning with multiple disks has always been a problem, but wasn't so serious previously, since the user would just be warned about having more operating systems on the disk than they really had. It became more dangerous when combined with Windows not being detected. A two disk setup of first disk with (undetected) EFI Windows and second disk with Ubuntu is handled as a "single OS Ubuntu upgrade", and when the user clicks to upgrade, the Windows disk is wiped.