Boot from VHD on WIndows 8 – Boot entry disappears occasionally

I had created a bootable windows 7 VHD. I am running Windows 8 Pro on my host machine. I followed the instructions from this link http://blogs.technet.com/b/haroldwong/archive/2012/08/18/how-to-create-windows-8-vhd-for-boot-to-vhd-using-simple-easy-to-follow-steps.aspx to boot from my VHD. This is really very simple and helpful article.
Everything was fine and I was able to see 2 options in my boot loader, 1. My Windows 8 Pro, 2. The newly added bootable Windows 7 VHD.

But in few days the windows 7boot option was not showing the the boot loader. Whenever I start my computer, it used to start windows 8 without showing the boot loader options. I followed the same procedure as mentioned in the above link but the boot loader still did not show up.

I noticed that my windows 8 has some pending updates showing in the notification area. As usual, I installed all the windows 8 updates and restarted my computer. Surprising this time, I was able to see the boot loader, and my Windows 7 VHD option was also showing in the boot menu.

After few days googling, I still could not find the reason behind this. But I was sure that whenever windows 8 has some pending updates, it just blocks the boot loader option (or it might be actually disabling the VHD boot options temporarily). Anything is possible, and I still do not the actual reason.
If anyone is facing the same situation then they can install all pending updates from their host PC and try.