Graphics Issue in Lion (MBP 13" Mid 2010)?!

I installed Mac OS X Lion without any problems, but if I drag a file from the Finder to the right side of my desktop, I get a graphical defect for about 0.5s!

I was able to make a snapshot:

This defect only appears if there are min. two columns on my desktop. I also tried to reinstall Lion, but the problem last!

How to solve it?