I think it's becoming clear that to multi boot will take a new type of boot manager. In future, in my humble opinion, Windows, Linux and any other OS will have to be installed on different hard drives and not on partitions within the hard drive. I don't know what is really going on but think Microsoft is going for the "Apple" type of issuing new OSs.

I might be totally wrong, of course.

Luckily the Open Source community has worked hard at resolving the issues created by proprietary people trying to lock down the hardware we purchase with our hard earned dollars for themselves. In Ubuntu try the Boot-Repair found in the standard ppa