Strange, i am dual booting, Windows 8.1 and Windows 10 v9860. I have the option every time to select. So not sure why your having issues.. but v9841 worked fine also.
I also lost the multiboot after update to 9861, but in msconfig the items were all there, so changed to win7 as default, then it booted to the b/w menu and went well.
i dual boot windows 8.1 and windows 10 on my laptop and 10.10 os x and windows 10 flawlessly thanks to my bios mod with ozmosis
The use of Ozmosis is quite dangerouse and works on sudden MB's only. Only for really Geek's to use tha way never an an Novice or literate User should even ever think about to use it!
I tried again from scratch: after making WU, disappears when you restart the dualboot (W7) and don't start nothing ... mystery
So far multi-boot: XP Pro x64, Win7 Ultimate w/SP1, Win8.1 Pro, and Win10 TP (all 64bit) works as expected with boot menu at startup/reboot. (Using EasyBCD 2.2.0.182)
My quad boot system is working fine with Win 10 TP + latest updates. The other OS's are XP Pro x32 SP3, Vista Ultimate x64 and Win 7 Ultimate x64.
so far ozmosis works on laptops with uefi and from z77 to x99 mobo's and it's super easy to use safe to say things have changed
I still do not understand With W7, W8, W8.1 ... no worries, with W10 TP idem, but after WU don't boot regularly. Maybe it's different from the installation ISO constructed that no normal upgrade? If i Upgrade with Microsoft channel I say you can not boot from vhd Amen
Create the Yosemite bootdisk with unibeast from the VMWARE MAC OS (if you don't have MAC yosemite bootdisk). Run that bootdisk from diskutil, you can create many partitions you like. Then install Windows 10, MAC, Linux....