Windows 7 - Power save sometimes doesn't turn off monitors

I just did a fresh install of Windows 7 home ultimate 64 bit and I am pretty sure this problem started right away...

I have an NVIDIA GeForce 6800 with a dual monitor setup - HP LP2475w connected via DVI, and a Samsung Syncmaster connected via VGA.

The problem is that when the system has been idle long enough and the monitors are supposed to power off, about half the time (unpredictable), although the monitors go black, they don't turn off (the backlight is on and the power LEDs show they are on).

Both monitors show the same behavior at the same time (e.g. either both will power off correctly, or both will fail to power off), so the problem isn't monitor-specific.

Back when I had XP on this same setup, I didn't have this problem.

Anybody experiencing a similar issue or have any ideas what might be the problem here? I started with Windows standard drivers but them installed NVIDIA's drivers, but it made no difference.

Windows 7 home ultimate 64-bit
Athlon 64
4GB
NVIDIA GeForce 6800

I think I found the problem - it's the Google Photos Screensaver included with Picasa 3. If I don't use that screensaver, the problem never occurs.