I have the SAME PROBLEM!
In Windows XP and a lower generation card - I am able to customize the display i.e. (Display 1 and Display 2 OR Display 2 and Display 1) in other words you can FREELY choose which one is designated Primary or #1. REPEAT in Windows XP there is no such issue.
For some CRAZY, reason you can only ASSIGN which one you want temporarily, Windows 7 seems to assign my reciever (Denon 989) as #1 (no option to change) - when all devices are powered on, you can freely choose mix and match.
The second I turn off my TV (hdmi through to receiver) I'm locked into extended view (although assigned as primary) but has flipped back. This is entirely depend on power on and off. Insanely frustrating is that I'm trapped in extended view "Windows P" toggle does not work and you cannot access settings - so I have to power my TV to get control back.
I'm at a loss as to why this is - again, XP works fine. I went to my computer store and they gave me a load of BS about HDMI compliancy blah, blah, blah....but I think the blame squarely lies on the developers of Windows 7 who feel they need to change everything (i.e. show desktop icon, move that to the right and not make it available on the left).
If anyone knows a simple fix, please tell me. I'm tired of rebooting and recofiguring my settings ad nauseum.
Also if any MS moderator is listening out there...I have spent hours trying to make my displays function properly, moving from nvidia cards to ati and so I know this issue intimately. I'm wondering who I can send an invoice for my time to?