Since I've upgraded my iPhone to OS4 I noticed a buggy behavior in my web-app:
When rotating to landscape and then back to portrait the view remains with the landscape zoom, causing only part of the page to be visible.
The problem appears only when viewing the application in full-screen mode. Try adding the sample web-app I made from the following link to your iPhone home screen. Then launch it, rotate to landscape and then back to portrait.
Is this a known bug? Any ideas for a workaround?