It's a "feature" on these monitors. I have that on my 2007WFP and I have seen persistent images on other S-IPS 2007WFP's. Nothing to worry about, and no need to return it. Luckily it's not very visible in normal use and the images disappear quite fast.
You can also find it out by doing this simple test.
1. Use dead pixel buddy or something else to make the screen black (or just change the desktop background black, or use some screensaver that makes the screen black).
2. Look the monitor from angle (something like 150 degrees)
3. If the...
Mine 2007WFP (A03, S-IPS, Czech, Jan 2007) flickers on greys when brightness is set below 40%. More visible on lower brightness (for example 20%). It flickers also with that test pattern, like it should. I still love this monitor, but I'm hoping that someone could confirm if there are coming...