Dual Display - "Turn of display after "x" minutes" issue

Hi I am running W7 64 Pro on a Ati HD 5750 GFx card my Dual displays (Dell SP2309W) are both connected with DVI.
All latest drivers are installed.
My issue is with the power-saving: when ever my displays are going to turn off automatically only one of my displays go to standby and the other just turns black. I can see the difference in the back light and the fact that the power button is still in active mode.

I'm not sure that it is entirely due to Dual displays though as I was running prime95 on my pc the other day i had it hooked up to another screen (only one monitor) and the standby led on the screen didn't change when it went black.

I don't like the fact that my screens don't turn themselves on standby as my computer uses enough power as it is.

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