I have a strange problem. I am very good with Macs and all Apple products, but this one has me stumped. 

I have a new (4 months old) 27" iMac (2.7 GHz Intel Core i5) with Lion 10.7.2 

and it works beautifully, but it does one thing that drives me crazy. After it has gone to Sleep, and I wake it up to use it, the screensaver pic or Lion Grey linen image stays on the screen and I have to scrub away some of it with my pointer/cursor to see the user login screen, almost like scratching away some frost to be able to see through my car's windshield in the winter.

What is causing this? And what can I do to get it to stop? I have had Macs forever and have never had this problem.

![enter image description here](https://i.stack.imgur.com/ewYr9.jpg)

![enter image description here](https://i.stack.imgur.com/OIKmY.jpg)