Mail won't rotate while turned iPad sideways

After I update my iPad 3G to iOS 4.2.1, I'm not able to have Mail rotate while turning iPad sideways, but other apps rotate and lock with the software new switch. The Mail is just stuck in the landscape mode and can't recognize portrait mode. I has enabled the rotation function in the setting.If you have the same issue, just shutdown and then restart your iPad. The Mail screen will operates