I have a strange problem, I believe I might just need some entitlement to declare to make it work.
I have some text view that user could copy text, and it could be pasted into another text fields inside the app. But when the user exit (or suspend ) the app, the user has no content in the clipboard and could not paste the text into another app. ( Such as, the user copied an URL from my app, but when he try to paste it inside Safari, nothing could be paste , the clipboard is empty).
[UPDATED] I found the problem and some discussion here: https://stackoverflow.com/a/8442428/140860