Seg fault in QQmlObjectCreator::finalize when creating QML object with initial bindings

class X : public QObject {
    Q_OBJECT
    QML_ELEMENT
    Q_PROPERTY(int x READ x WRITE setX BINDABLE bindableX)
    Q_OBJECT_BINDABLE_PROPERTY(X, int, _xProp)

public:
    int x() const { return _xProp.value(); }
    void setX(int x) { _xProp.setValue(x); }
    QBindable<int> bindableX() const { return &_xProp; }
};

import BT
import QtQuick

Item {
    property int v: 0
    property X xthing: X {
        x: v
    }
}