There have been lots of reports about the iPod touch not rotating correctly from landscape to portrait or back. I think I know why.
Firstly, its to do with the fact they use an accelerometer. The X/Y axis sensing won’t work if the device is too flat. It has to account for general movement so there is a threshold for rotation. That can be improved in software but never perfect.
I think also, a lot of problems are from people touching the screen DURING rotation. It seems you can “Catch” the image at any angle while its rotating and it stays there. Its fairly easy to get about a 45′ tilt on a picture. You will also see it get confused over orientation while trying, exhibiting the rotation bug.
Here is a video to show what I mean, you can see both the failure to rotate, getting stuck in the wrong orientation and the 45’grab bug.
Bug? Feature? Soft or hardware? You decide. Click on the image below for video.