Any idea what this displayport error message is ? Asus PB278Q

[The Matrix]

Occasionally i turn my monitor off via the power button on the monitor but leave the pc switched on, i'm getting the following message when i turn the monitor back on after its been switched off whilst using displayport, this doesn't happen when its connected via a Dual link DVI cable. If you reboot the PC their is no error message, its only happening if you switch the monitor off for a short time then switch it back on. Any ideas what the error is ?

 

[The Matrix]

My GPU is a single Sapphire 7970 3GB Vapor X, as i said it doesn't do it with a Dual link DVI cable.

I'm thinking that its something to do with when you turn the monitor off at the power button, for some reason when you turn it back on it doesn't fully detect the Displayport cable, it still displays 2560 x 1440 but their maybe an error in the way the monitor detects the cable when you power it off and then turn it back on.

I'd be interested to hear from anyone else with an Asus PB278Q if their's does the same with the displayport cable attached.