iPhone SDK: How to centre content in a UIScrollView during setZoomScale?

Question

I'm using a UIScrollView to show photos. If they are zoomed out so they are smaller than the scroll view in one dimension then the content is centred using contentInset and contentOffset. This all works fine for scrolling and manual zooming.

However, if I use setZoomScale (with animated YES) then when zooming out the scroll view sets the top left edge to 0,0 during the animation and then snaps it back afterwards. It seems like the zoom animation ignores the contentInset and contentOffset settings.

Does anyone have any idea how to overcome this problem?

Thanks,

Russell.