QListWidgetItem appearance in 4.7

I just upgraded from Ubuntu 10.04 to 10.10,
therefore : python 2.6.5 + Qt 4.6 + PyQt 4.7.2 to python 2.6.6 + Qt 4.7 + Pyqt 4.7.4

It seems that the appearance of the QListWidgetItem changed.

In my code, I apply a styleSheet on the QlistWidget (color: white; background: black),
I've tried with other parameters, in Maverick(10.10), the items appears always in a withe rectangle.

I joint two images which show the problem.
Old appearance : lucid.jpg
New (and bad) appearance : maverick.jpg

Vincent