Line number in warning is random and out of bounds

import QtQuick
import QtQuick.Controls

ApplicationWindow {
    id: window
    width: 640
    height: 480
    visible: true

    MonthGrid {
        delegate: Text {
            horizontalAlignment: Text.AlignHCenter
            verticalAlignment: Text.AlignVCenter
            opacity: month === month ? 1 : 0
            text: day
            font: control.font

            required property int day
            required property int month
        }
    }
}