I guess what you are saying is that you moved the bootmgr from OS1 to OS2. I am still not sure though how that cleans up the MBR (Steps 4 and 5 in my tutorial).Moved that @ the onset to OS2. Notice, boot functionality was checked (& proven) by booting into OS2 w/out the OS1 drive connected to the M/B. And the OS1 partition completely renewed.
Watch out that you really can get a dual boot. I never had the chance to select anything. It just rolled along and upgraded my Windows7. But since I am always careful, I had made an image before mucking around with it. So it was no problem to get things back in order.I didn't know about, hadn't seen the tutorial when or before what I did & passed on to others. More than 1 way to skin a cat... (?)
Now, having just burnt the ISO to DVD, I'm about to install Win8 Beta (no more DP) & dual-boot Win8 & Win7, both x64.