I'am a registerd dev and I have used the ios7 beta's and have yet to encounter this problem. When you put safari in private browsing mode there is a shadow that appears on the left side of the screen when the device is in landscape mode. The shadow immediately disappears as soon as you start to scroll the page or if you change the phones orientation. I haven't been able to find anything on the web about this bug and wanted to know if anyone running the GM can reproduce it. I've tried on two different iPhone 5's and the issue is present on both.