UIScrollView with paging enabled: strange behavior when swiping left or right

I have a UIScrollView and it has paging开发者_JS百科 enabled (vertically). Swiping up or down scrols to the previous or next page as expected. However when swiping left or right, the previous or next page is shown without any animation. I cannot find a setting to disable this! The view is exactly as wide as the surrounding view. It only scrolls vertically. What's the best approach?