5.4.0
"MainWindow" QEnterEvent(QPoint(73,92))
void QWidgetWindow::handleEnterLeaveEvent(QEvent*) calling dispatchEnterLeave() 2)
static void QApplicationPrivate::dispatchEnterLeave(QWidget*, QWidget*, const QPointF&) > QGroupBox(0x2472910, name = "GroupBox") QObject(0x0) 
QApplicationPrivate::dispatchEnterLeave, ENTER: QGroupBox(0x2472910, name = "GroupBox") LEAVE: QObject(0x0) 
QApplicationPrivate::dispatchEnterLeave2, ENTER: (QMainWindow(0x7fffdd51db80, name = "Main") ,  QGroupBox(0x2472910, name = "GroupBox") )  LEAVE: ()
"Main" QEnterEvent(QPoint(73,92))
"GroupBox" QEnterEvent(QPoint(73,92))
static void QApplicationPrivate::dispatchEnterLeave(QWidget*, QWidget*, const QPointF&) < QGroupBox(0x2472910, name = "GroupBox") QObject(0x0) 
static bool QApplicationPrivate::sendMouseEvent(QWidget*, QMouseEvent*, QWidget*, QWidget*, QWidget**, QPointer<QWidget>&, bool) calling dispatchEnterLeave 2)
static void QApplicationPrivate::dispatchEnterLeave(QWidget*, QWidget*, const QPointF&) > QLabel(0x25068b0, name = "Label") QGroupBox(0x2472910, name = "GroupBox")
QApplicationPrivate::dispatchEnterLeave, ENTER: QLabel(0x25068b0, name = "Label") LEAVE: QGroupBox(0x2472910, name = "GroupBox")
QApplicationPrivate::dispatchEnterLeave2, ENTER: (QLabel(0x25068b0, name = "Label") )  LEAVE: ()
"Label" QEnterEvent(QPoint(59,51))
static void QApplicationPrivate::dispatchEnterLeave(QWidget*, QWidget*, const QPointF&) < QLabel(0x25068b0, name = "Label") QGroupBox(0x2472910, name = "GroupBox")
"MainWindow" QMouseEvent(MouseButtonPress, LeftButton, localPos=QPointF(70,61), screenPos=QPointF(472,384))
static bool QApplicationPrivate::sendMouseEvent(QWidget*, QMouseEvent*, QWidget*, QWidget*, QWidget**, QPointer<QWidget>&, bool) assigning leaveAfterRelease= QLabel(0x25068b0, name = "Label")
"Label" QMouseEvent(MouseButtonPress, LeftButton, localPos=QPointF(58,31), screenPos=QPointF(472,384))
"GroupBox" QMouseEvent(MouseButtonPress, LeftButton, localPos=QPointF(70,61), screenPos=QPointF(472,384))
virtual void QXcbWindow::handleLeaveNotifyEvent(const xcb_leave_notify_event_t*)
virtual void QXcbWindow::handleLeaveNotifyEvent(const xcb_leave_notify_event_t*) calling QWindowSystemInterface::handleLeaveEvent() 2)
static void QGuiApplicationPrivate::processLeaveEvent(QWindowSystemInterfacePrivate::LeaveEvent*)
Leave with mouse down # 0 "MainWindow"
void QWidgetWindow::handleEnterLeaveEvent(QEvent*) calling dispatchEnterLeave() 1)
static void QApplicationPrivate::dispatchEnterLeave(QWidget*, QWidget*, const QPointF&) > QObject(0x0)  QLabel(0x25068b0, name = "Label")
QApplicationPrivate::dispatchEnterLeave, ENTER: QObject(0x0)  LEAVE: QLabel(0x25068b0, name = "Label")
QApplicationPrivate::dispatchEnterLeave2, ENTER: () LEAVE: (QLabel(0x25068b0, name = "Label") ,  QGroupBox(0x2472910, name = "GroupBox") ,  QMainWindow(0x7fffdd51db80, name = "Main") ) 
Leave with mouse down # 1 "Label"
Leave with mouse down # 2 "GroupBox"
Leave with mouse down # 3 "Main"
static void QApplicationPrivate::dispatchEnterLeave(QWidget*, QWidget*, const QPointF&) < QObject(0x0)  QLabel(0x25068b0, name = "Label")

--------------> Additional leave on mouse release is received from X11:

virtual void QXcbWindow::handleLeaveNotifyEvent(const xcb_leave_notify_event_t*)
virtual void QXcbWindow::handleLeaveNotifyEvent(const xcb_leave_notify_event_t*) calling QWindowSystemInterface::handleLeaveEvent() 2)
"MainWindow" QMouseEvent(MouseButtonRelease, LeftButton, localPos=QPointF(70,130), screenPos=QPointF(472,453))
"Label" QMouseEvent(MouseButtonRelease, LeftButton, localPos=QPointF(58,100), screenPos=QPointF(472,453))
"GroupBox" QMouseEvent(MouseButtonRelease, LeftButton, localPos=QPointF(70,130), screenPos=QPointF(472,453))
"Main" QMouseEvent(MouseButtonRelease, LeftButton, localPos=QPointF(70,130), screenPos=QPointF(472,453))
static bool QApplicationPrivate::sendMouseEvent(QWidget*, QMouseEvent*, QWidget*, QWidget*, QWidget**, QPointer<QWidget>&, bool) leaveAfterRelease= QLabel(0x25068b0, name = "Label") mouseGrabber= QObject(0x0) 
static bool QApplicationPrivate::sendMouseEvent(QWidget*, QMouseEvent*, QWidget*, QWidget*, QWidget**, QPointer<QWidget>&, bool) calling dispatchEnterLeave 3)
static void QApplicationPrivate::dispatchEnterLeave(QWidget*, QWidget*, const QPointF&) > QMainWindow(0x7fffdd51db80, name = "Main") QLabel(0x25068b0, name = "Label")
QApplicationPrivate::dispatchEnterLeave, ENTER: QMainWindow(0x7fffdd51db80, name = "Main") LEAVE: QLabel(0x25068b0, name = "Label")
QApplicationPrivate::dispatchEnterLeave2, ENTER: () LEAVE: (QLabel(0x25068b0, name = "Label") ,  QGroupBox(0x2472910, name = "GroupBox") ) 
Leave with mouse up   4 "Label"
Leave with mouse up   5 "GroupBox"
static void QApplicationPrivate::dispatchEnterLeave(QWidget*, QWidget*, const QPointF&) < QMainWindow(0x7fffdd51db80, name = "Main") QLabel(0x25068b0, name = "Label")
static void QGuiApplicationPrivate::processLeaveEvent(QWindowSystemInterfacePrivate::LeaveEvent*)
Leave with mouse up   6 "MainWindow"
void QWidgetWindow::handleEnterLeaveEvent(QEvent*) calling dispatchEnterLeave() 1)
static void QApplicationPrivate::dispatchEnterLeave(QWidget*, QWidget*, const QPointF&) > QObject(0x0)  QMainWindow(0x7fffdd51db80, name = "Main")
QApplicationPrivate::dispatchEnterLeave, ENTER: QObject(0x0)  LEAVE: QMainWindow(0x7fffdd51db80, name = "Main")
QApplicationPrivate::dispatchEnterLeave2, ENTER: () LEAVE: (QMainWindow(0x7fffdd51db80, name = "Main") ) 
Leave with mouse up   7 "Main"
static void QApplicationPrivate::dispatchEnterLeave(QWidget*, QWidget*, const QPointF&) < QObject(0x0)  QMainWindow(0x7fffdd51db80, name = "Main")