DVI monitor detected but not activated after extended "off" state

I have a dual monitor setup, one VGA, one DVI. Monitors are set to power off after 30 minutes of inactivity. Sleep mode is set to 'never'.

When I walk away for an extended time (as short as 1 hour), the monitors go off as expected, but when I come back and touch the mouse, only the VGA monitor wakes up. DVI monitor continues to stay asleep.

Both NVIDIA Control Panel and Windows "Screen Resolution" panel report the presence of the DVI monitor, but it is deactivated.

Rebooting restores both monitors, usually. (Though now the desktop icons appear on the secondary monitor instead of the primary, which confuses me too.)

Dell Latitude E6520, docked

Windows 7 Pro 64-bit

Nvidia NVS 4200M

In BIOS, Optimus technology is unchecked. (This causes only the Nvidia adapter to appear in Device Manager. Checking it results in both Nvidia and Intel appearing in Device Manager.)

Dell System Detect and Windows Device Manager both tell me the Nvidia driver is up to date. Nvidia's detector tells a different story.

Anyone have any ideas what's going on here?

Thanks
Jeff