Sporadic crash on QFontEngineMulti::ensureEngineAt()

Exception Type:  SIGSEGV
Exception Codes: SEGV_MAPERR at 0x20
Crashed Thread:  0

Thread 0 Crashed:
0   QtGui                                0x00000001188721e5 QFontEngineMulti::ensureEngineAt(int) (qfontengine.cpp:1765)
1   QtGui                                0x00000001188732e6 QFontEngineMulti::getGlyphBearings(unsigned int, double*, double*) (qfontengine.cpp:2008)
2   QtGui                                0x00000001189069ec QTextLine::layout_helper(int) (qtextlayout.cpp:1734)
3   QtQuick                              0x000000011714283c QQuickTextPrivate::setLineGeometry(QTextLine&, double, double&, bool) (qquicktext.cpp:1332)
4   QtQuick                              0x000000011713fe3a QQuickTextPrivate::setupTextLayout(double*) (qquicktext.cpp:1004)
5   QtQuick                              0x000000011713ba4d QQuickTextPrivate::updateSize() (qquicktext.cpp:390)
6   QtQuick                              0x000000011713dce1 QQuickTextPrivate::updateLayout() (qquicktext.cpp:269)
7   QtQuick                              0x00000001171438c4 QQuickText::setText(QString const&) (qquicktext.cpp:1871)
8   QtQml                                0x0000000119b81ca7 GenericBinding<10>::write(QV4::Value const&, bool, QFlags<QQmlPropertyData::WriteFlag>) (qqmlpropertydata_p.h:339)
9   QtQml                                0x0000000119b7f908 QQmlBinding::doUpdate(QQmlJavaScriptExpression::DeleteWatcher const&, QFlags<QQmlPropertyData::WriteFlag>, QV4::Scope&) (qqmlbinding.cpp:0)
10  QtQml                                0x0000000119b7d7ab QQmlBinding::update(QFlags<QQmlPropertyData::WriteFlag>) (qqmlbinding.cpp:164)
11  QtQml                                0x0000000119c0deca QQmlNotifier::emitNotify(QQmlNotifierEndpoint*, void**) (qqmlnotifier.cpp:70)
12  QtCore                               0x000000011a6205b0 void doActivate<false>(QObject*, int, void**) (qobject.cpp:3884)
13  QtQmlModels                          0x00000001157e3a94 VDMModelDelegateDataType::notify(QQmlAdaptorModel const&, QList<QQmlDelegateModelItem*> const&, int, int, QList<int> const&) const (qqmladaptormodel.cpp:139)
14  QtQmlModels                          0x00000001157f14f7 QQmlDelegateModel::_q_itemsChanged(int, int, QList<int> const&) (qqmladaptormodel_p.h:127)
15  QtQmlModels                          0x00000001157f4918 QQmlDelegateModel::_q_layoutChanged(QList<QPersistentModelIndex> const&, QAbstractItemModel::LayoutChangeHint) (qqmldelegatemodel.cpp:2007)
16  QtQmlModels                          0x00000001157fe0cd QQmlDelegateModel::qt_metacall(QMetaObject::Call, int, void**) (moc_qqmldelegatemodel_p.cpp:612)
17  QtCore                               0x000000011a62083e void doActivate<false>(QObject*, int, void**) (qobject.cpp:4018)
18  QtCore                               0x000000011a7fa042 QAbstractItemModel::layoutChanged(QList<QPersistentModelIndex> const&, QAbstractItemModel::LayoutChangeHint) (moc_qabstractitemmodel.cpp:1331)
19  QtCore                               0x000000011a825a3d QSortFilterProxyModelPrivate::_q_sourceDataChanged(QModelIndex const&, QModelIndex const&, QList<int> const&) (qsortfilterproxymodel.cpp:1492)
20  QtCore                               0x000000011a620b2a void doActivate<false>(QObject*, int, void**) (qobject.cpp:4004)
21  QtCore                               0x000000011a7f9f6c QAbstractItemModel::dataChanged(QModelIndex const&, QModelIndex const&, QList<int> const&) (moc_qabstractitemmodel.cpp:1317)
...

void QFontEngineMulti::ensureEngineAt(int at)
{
    if (!m_fallbackFamiliesQueried && at > 0)
        ensureFallbackFamiliesQueried();
    Q_ASSERT(at < m_engines.size());
    if (!m_engines.at(at)) {
        QFontEngine *engine = loadEngine(at);
        if (!engine)
            engine = new QFontEngineBox(fontDef.pixelSize);
        Q_ASSERT(engine && engine->type() != QFontEngine::Multi);
        engine->ref.ref();
        m_engines[at] = engine; <-- CRASHED HERE
    }
}