QDockWidget doesn't draw correctly in QCleanLooks style

The bottom border of the QDockWidget bar doesn't appear when using a layout with 0 margins in QCleanLooks

To reproduce:
open Qt designer
create a widget with a QDockWidget inside
Add a QListWidget into the QDockWidget
Remove the frame to the QListWidget
Set a layout to the QDockWidget (vertical?) with a margin of 0 for the top
Preview in Cleanlooks
->the bottom border of the QDockWidget doesn't show up