Screen distortion issue upon rotating iPhone 4

Hello all.
I finally got my iPhone and Im currently in the phase of being paranoid about every single action takes place inside the phone. But this one may actually be a problem.
When I open Safari when Im not connected to 3G or WiFi, an untitled page opens up. When I rotate the phone, the page is displayed horizontally, no problem. When I rotate it back to display it vertically, just for a fraction of a second, I see black and white patterns (like a checkerboard) at the lower portion of the screen. But after that instantenous moment, everything is normal.
Is this a known issue? Or Im starting with the RMA stuff
iPhone 4 iOS 4