QGLWidget creation with parent triggers warning/crash

I use a class derived from QGLWidget:

GLChannel::GLChannel(qint32 channel, QGLWidget *shareWidget, QWidget *parent)
: QGLWidget(parent,shareWidget)
{

}

if I pass a parent widget, I get this warning message (though the app work):
"WindowCreationData::create: CreateWindowEx failed (Impossible de créer une fenêtre enfant supérieure.)"
(the end of the message can be translated to: "can't create a higher child window")

If I pass a NULL parent, I don't get the error message.

This happen with this Qt 5.1 build on Windows:
http://download.qt-project.org/snapshots/qt/5.1/5.1.0-rc1/backups/2013-05-29-41/

I don't have this warning with Qt 5.0.2