Why won't Windows save my multi-monitor settings?

I've seen this happen occasionally, and usually it's a problem with the initial monitor enumeration. Oftentimes changing to a much newer or older driver revision might fix it - specifically with that card, try removing the Nvidia driver ENTIRELY and just use the one that comes out-of-the-box with Windows 7.

Alternatively, since this is only two monitors, you might just consider physically reversing the manner in which they're cabled (so it enumerates them in the opposite order).

(If this has always been a problem with this machine, it's possible it's something screwy with this particular GPU, I guess. You could always use Displayfusion or Ultramon or something to automate the process of reversing the order of the screens with a hotkey or the like.)

I got an email notification that a new driver was available, so I did the update and selected the 'clean install' option. The problem has now gone and my monitor configuration is being persisted correctly. Ho hum.