I found "Modal View Controller" could have some changes in iOS4. Because, I used the example code below http://iosdevelopertips.com/video/getting-mpmovieplayercontroller-to-cooperate-with-ios4-3-2-ipad-and-earlier-versions-of-iphone-sdk.html
to perform the movie player controller using button. In iOS3, the page control still can work after dismiss modal view controller. But in iOS4 is not, I need to press the navigation bar on the upper-left corner to go back and then click the cell back to the view, then page control will work again.
What is the main reason causing this problem?