I'm not sure I get where there is a question, here. What is it your asking??
If, this has anything to do w/ it...
I've had duel-boots, a triple for a while, too, but, anyway, since the XP Vista overlap during & after I was beta-testing Vista. Once there are 2 machines in place & 2 show on the choice screen & choose 1 & go & they are listed A & B. Whichever goes from Highlight to Enter doesn't matter... nothing should reboot or go through some cycling or … should just directly start up whichever one (the same).
And, I can tell you that if, you change the boot priority, making B boot '1st', if you don't hit anything before so many seconds
Then, @ the choice screen, they will, still, be listed A (on top) & B but, now B will be the one starting
I dunno if I'm saying anything you don't already know AND if it even points @ the query.
And, if Win 7 was in the box 1st, it has the Boot. If, you pulled the plug on 7, 8 would no longer boot. The Boot is where the 1st OS installed is, it's w/ the 1st OS put in the machine.
If you change the Boot priority so 7 started 1st... @ the choice screen 8 would still be listed as it was, on top & 7 underneath, 2nd so to speak BUT... because you are seeing it on top you think it's using 8's Boot, it's not. Now 7 would go to start 1st but, 8 would ,still be listed 1st but, the highlight would now be @ 7, positioning doesn't change.
If it, Win8, was installed on a machine 1st or by itself then it hold the Boot. If you duel-booted & 8 was 1st in the box then it would have the Boot not, 7; cus 8 got there 1st, in that scenario.
Here... I installed Win7 x86 then, Win7 x64, afterwards. When I wanted to wipe out the x86, had to move the Boot from it to the x64.
Until then, you can't boot B w/out A.
God, I trust this is making sense. Or it's clear as mud. We're not sure, @ this point...tell me later
Cheers,
Drew