I have two U2414H monitors connected to my 2010 Mac Pro via AMD Radeon HD7950 DisplayPort using Dell supplied cables. Running OS X 10.9.2.
Sleeping the computer does turn off the displays...temporarily. At varying intervals, one or the other (but usually not both) display will 'wake' into the B&W dialog box screen showing "DisplayPort" and the DP icon. Rather troublesome when you have to share your bedroom with them. The easy solution is manually powering them down, but sometimes I sleep the computer e.g. mid-day and forget about the monitors.
Anyone else encounter this?