Qt textedit input method problem. please help!

I am using Qt 4.6 now, It's nice for work. But I meet with one big problem that when I using input method. The problem is something like this:

I have a QGraphicsView which content a widget that only have a QTextEdit control in it. When I want to switch English input method to Chinese input method there is no response. I don't know why, for it works very well under Qt 4.5.2. And Anybody knows how to enable input method in QTextEdit please tell me. Thanks for any idea.

yours Scott.