Hi
Just came here as I have the same issue.
Intel board: DZ77BH-55K with Intel i7 3770, Windows 7 64Bit
DELL monitor connected by DisplayPort, second LCD monitor connected by DVI.
DELL monitor does not sleep or standby when told to by Windows, LCD monitor on DVI does.
Problem only with the latest Intel graphics drivers version 9.18.10.316, rolling back to the previous drivers and the monitor behaves normally and switches to standby.
By the way the new Intel Control panel is hideous using the Windows 8 style of all white space and huge graphics, I've stayed with Windows 7 for a reason!
Regards
Phil