When I have my usb printer plugged into the back of my iMac and the screen dims for energy saving, it doesn't brighten all over when I wake it. It's mostly dim with one bright spot in bottom left. Only a restart will brighten the screen. Without the printer plugged in it always brightens evenly. I cannot plug the printer into my keyboard as it's wireless. Anyone else have problems with a usp device plugged into the back of their iMac??