QListWidget + setWindowFlags = bad scrollbar

[trallallero]

I create a modal gui just to show a list with a QListWidget.
This is the class:

class CShowRolesModalGui : public QDialog
{
	Q_OBJECT
 
	public:
		CShowRolesModalGui(const QStringList& items, QWidget* parent);
 
	private slots:
		void Close () { done(0); }
};

class CShowRolesModalGui : public QDialog
{
	Q_OBJECT

	public:
		CShowRolesModalGui(const QStringList& items, QWidget* parent);

	private slots:
		void Close () { done(0); }
};

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and this is the code:

CShowRolesModalGui::CShowRolesModalGui(const QStringList& items, QWidget* parent) : QDialog(parent)
{
	setGeometry(QRect(QPoint(205, 430), QSize(400, 300)));
	setFixedSize(400, 300);
	setStyleSheet(ROLES_WIDGET_STYLE);
	setWindowFlags(Qt::FramelessWindowHint);
 
	QListWidget* listView = new QListWidget(this);
	listView->setGeometry(2, 2, 396, 260);
	listView->setStyleSheet(LIST_SHOW_ROLE_STYLE);
	listView->addItems(items);
 
	QPushButton* btn = new QPushButton(tr("Ok"), this);
	btn->setGeometry(175, 265, 50, 30);
	btn->setStyleSheet(FREQ_MODAL_BTN_STYLE);
	connect(btn, SIGNAL(clicked()), this, SLOT(Close()));
}

CShowRolesModalGui::CShowRolesModalGui(const QStringList& items, QWidget* parent) : QDialog(parent)
{
	setGeometry(QRect(QPoint(205, 430), QSize(400, 300)));
	setFixedSize(400, 300);
	setStyleSheet(ROLES_WIDGET_STYLE);
	setWindowFlags(Qt::FramelessWindowHint);

	QListWidget* listView = new QListWidget(this);
	listView->setGeometry(2, 2, 396, 260);
	listView->setStyleSheet(LIST_SHOW_ROLE_STYLE);
	listView->addItems(items);

	QPushButton* btn = new QPushButton(tr("Ok"), this);
	btn->setGeometry(175, 265, 50, 30);
	btn->setStyleSheet(FREQ_MODAL_BTN_STYLE);
	connect(btn, SIGNAL(clicked()), this, SLOT(Close()));
}

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If I call the function setWindowFlags (and I have to call it as I don't want a gui with a border), the QListWidget's scrollbar is visible but doesn't work with the mouse buttons, only with the wheel and the keyboard.

How can I solve the problem ? I really need a GUI without a border.
Thanks.

PS: I doesn't work also with:
setWindowFlags(windowFlags() | Qt::FramelessWindowHint);
setWindowFlags(Qt::FramelessWindowHint);
setWindowFlags(Qt::CustomizeWindowHint);
and so on ...