assertion failed after Flickable takes grab from PinchHandler

6  QMessageLogger::fatal                                                qlogging.cpp              850  
7  qt_assert                                                            qassert.cpp               68   
8  QQuickDeliveryAgentPrivate::onGrabChanged                            qquickdeliveryagent.cpp   1712 
9  QtPrivate::FunctorCall<QtPrivate::IndexesList<0, 1, 2, 3>, QtPrivate qobjectdefs_impl.h        135  
10 QtPrivate::FunctionPointer<void (QQuickDeliveryAgentPrivate:: *)(QOb qobjectdefs_impl.h        172  
11 QtPrivate::QPrivateSlotObject<void (QQuickDeliveryAgentPrivate:: *)( qobject_p.h               285  
12 QtPrivate::QSlotObjectBase::call                                     qobjectdefs_impl.h        363  
13 doActivate<false>                                                    qobject.cpp               3972 
14 QMetaObject::activate                                                qobject.cpp               4032 
15 QPointingDevice::grabChanged                                         moc_qpointingdevice.cpp   410  
16 QPointingDevicePrivate::setExclusiveGrabber                          qpointingdevice.cpp       473  
17 QPointerEvent::setExclusiveGrabber                                   qevent.cpp                350  
18 QQuickFlickable::filterPointerEvent                                  qquickflickable.cpp       2579 
19 QQuickFlickable::childMouseEventFilter                               qquickflickable.cpp       2635 
20 QQuickDeliveryAgentPrivate::sendFilteredPointerEventImpl             qquickdeliveryagent.cpp   2383 
21 QQuickDeliveryAgentPrivate::sendFilteredPointerEventImpl             qquickdeliveryagent.cpp   2451 
22 QQuickDeliveryAgentPrivate::sendFilteredPointerEvent                 qquickdeliveryagent.cpp   2332 
23 QQuickDeliveryAgentPrivate::deliverUpdatedPoints                     qquickdeliveryagent.cpp   1912 
24 QQuickDeliveryAgentPrivate::deliverPointerEvent                      qquickdeliveryagent.cpp   1791 
25 QQuickDeliveryAgentPrivate::deliverDelayedTouchEvent                 qquickdeliveryagent.cpp   1234 
26 QQuickDeliveryAgentPrivate::flushFrameSynchronousEvents              qquickdeliveryagent.cpp   1601 
27 QSGThreadedRenderLoop::polishAndSync                                 qsgthreadedrenderloop.cpp 1480 
28 QSGThreadedRenderLoop::handleUpdateRequest                           qsgthreadedrenderloop.cpp 1347 
29 QQuickWindow::event                                                  qquickwindow.cpp          1521 
30 QCoreApplicationPrivate::notify_helper                               qcoreapplication.cpp      1193 
31 doNotify                                                             qcoreapplication.cpp      1122 
32 QCoreApplication::notify                                             qcoreapplication.cpp      1105 
33 QGuiApplication::notify                                              qguiapplication.cpp       1928 
34 QCoreApplication::notifyInternal2                                    qcoreapplication.cpp      1026 
35 QCoreApplication::sendEvent                                          qcoreapplication.cpp      1442 
36 QPlatformWindow::deliverUpdateRequest                                qplatformwindow.cpp       774  
37 QPlatformWindow::windowEvent                                         qplatformwindow.cpp       454  
38 QXcbWindow::windowEvent                                              qxcbwindow.cpp            2300 
39 QGuiApplicationPrivate::sendQWindowEventToQPlatformWindow            qguiapplication.cpp       1985 
40 QGuiApplication::notify                                              qguiapplication.cpp       1922 
41 QCoreApplication::notifyInternal2                                    qcoreapplication.cpp      1026 
42 QCoreApplication::sendEvent                                          qcoreapplication.cpp      1442 
43 QTimerInfoList::activateTimers                                       qtimerinfo_unix.cpp       610  
44 timerSourceDispatch                                                  qeventdispatcher_glib.cpp 149  
45 g_main_context_dispatch                                                                             
46 ??                                                                                                  
47 g_main_context_iteration                                                                            
48 QEventDispatcherGlib::processEvents                                  qeventdispatcher_glib.cpp 393  
49 QXcbGlibEventDispatcher::processEvents                               qxcbeventdispatcher.cpp   96   
50 QEventLoop::processEvents                                            qeventloop.cpp            100  
51 QEventLoop::exec                                                     qeventloop.cpp            182  
52 QCoreApplication::exec                                               qcoreapplication.cpp      1347 
53 QGuiApplication::exec                                                qguiapplication.cpp       1860 
54 main                                                                 main.cpp                  23