QGraphicsScene's bug? When a QTableWidget is embedded in the QGraphicsScene, the mouse shape is strange.

[Max.C]

I use Qt 4.6.2. A QTableWidget needs added into QGraphicsScene. Then, it is very strange that the mouse shape is always an arrow even if I adjust the column width on the table header(pic 1). But, if adding the table into the layout of a widget directly, the mouse shape becomes left-right arrow when adjusting the column width(pic 2, I want this effect).
Is it the bug of QGraphicsScene? Or, I just need some special settings.

!https://skydrive.live.com/?sc=photos&cid=b14f709aca22e062#cid=B14F709ACA22E062&id=B14F709ACA22E062!123&sc=photos()!
pic 1. mouse shape is just an arrow

!https://skydrive.live.com/?sc=photos&cid=b14f709aca22e062#cid=B14F709ACA22E062&id=B14F709ACA22E062!124&sc=photos()!
pic 2. mouse shape is the left-right arrow