iphone webview does not response until I hold on for about half a second

I created a web view in my iPhone app but every first time I open it (on my real device), I have to tap on the screen and hold on for about half a second, then the app can response to my touch events.

I don't know if this is some kind of mechanism or is something wr开发者_开发百科ong with my code.

(I use this web view to load some complex JavaScript and HTML, is there any CSS property or something else that could fix this problem?)