I've been looking at how wubildr.mbr works - it finds and uses the first wubildr by scanning the root of all partitions, in BIOS order. On my computer the C: drive is the second partition and it never uses C:\WUBILDR. It always uses the one on my recovery partition /dev/sda1.
So Grub2 is using the existence of /host/wubildr to tell if it's a Wubi install, but I can delete it and it still boots fine - it's an 'artifact' as cjwatson would say. Therefore it shouldn't harm anything to have another 'artifact' on the /host partition when Wubi isn't installed on the Windows partition. If Grub2 considers this a Wubi indicator, there should either always be a /host/wubildr (or it shouldn't consider it important at all - i.e. the fact that root is loopmounted on /host/ubuntu/disks/root.disk should be enough).
Note that when Grub2 does find /host/wubildr - it updates it - to be compatible with the latest grub changes. The problem is, the one it updates often isn't the one used to boot. It really should be doing what WUBILDR.MBR does - check each partition in order and update the first one it finds (and/or update all it finds). This might also explain the booting problems we've been seeing lately when Wubi is installed to the same partition as Windows (bug 682337)
I've been looking at how wubildr.mbr works - it finds and uses the first wubildr by scanning the root of all partitions, in BIOS order. On my computer the C: drive is the second partition and it never uses C:\WUBILDR. It always uses the one on my recovery partition /dev/sda1.
So Grub2 is using the existence of /host/wubildr to tell if it's a Wubi install, but I can delete it and it still boots fine - it's an 'artifact' as cjwatson would say. Therefore it shouldn't harm anything to have another 'artifact' on the /host partition when Wubi isn't installed on the Windows partition. If Grub2 considers this a Wubi indicator, there should either always be a /host/wubildr (or it shouldn't consider it important at all - i.e. the fact that root is loopmounted on /host/ubuntu/ disks/root. disk should be enough).
Note that when Grub2 does find /host/wubildr - it updates it - to be compatible with the latest grub changes. The problem is, the one it updates often isn't the one used to boot. It really should be doing what WUBILDR.MBR does - check each partition in order and update the first one it finds (and/or update all it finds). This might also explain the booting problems we've been seeing lately when Wubi is installed to the same partition as Windows (bug 682337)