Unsolved PyQt4 graphics : contextMenu does not appear if graphics item is not movable...

[ppuiseux]

In a QGraphicsScene, i first select some graphics item, say myitem, then I right-click on it the

scene().contextMenuEvent(self,event)

is called, and show the context menu i build there. All is right.

I execute this instruction :

myitem.setFlag(ItemIsMovable, False)

Now i right-click on (selected) myitem and context menu does not appear anymore...
Maybe I should show a complete program having this behaviour ?