I know this is an old thread but I wanted to offer the insight into this issue I gained last year when I tackled this problem. I forget where I found the solution but this thread led me there.
I have a late 2013 15" MBP Retina 512GB.
I've been able to get virtualization and hyper-v to launch/work 100% of the time when loading windows from OSX. I'm guessing when booting into OSX all of the processor's features are enabled and that translates over to windows when using Startup Disk to reboot.
Essentially this is the procedure I follow when I want to use hyper-v and it has yet to fail even through two separate Bootcamp installs.
From windows:
Right click the Bootcamp Assistant in the tray and choose reboot into OSX.
After it reboots into OSX I tend to select shut down and then power the computer back up from off letting it load into OSX for good measure.
Log in to OSX
Launch Startup Disk
Select restart to the Bootcamp partition.
Functional hyper-v
From OSX:
Restart the computer for good measure.
Log in to OSX
Launch Startup Disk
Select restart to the Bootcamp partition.
Functional hyper-v
I can't guarantee success to everyone but this has worked for me on my machine through two different Bootcamp installs and works on my friends MBP as well.