Setting Combobox currentIndex to -1 doesnt update view

import QtQuick 2.1
import QtQuick.Controls 1.0
import QtQuick.Layouts 1.0
import QtQuick.Window 2.0

ApplicationWindow {
  title: qsTr("ComboBox Test")
  width: 250
  height: 100

  ColumnLayout {
    Button {
      text: "reset currentIndex"
      onClicked: {
        combo.currentIndex = -1
      }
    }

    ComboBox {
      id: combo
      model: ["abc", "def", "ghi"]

      onCurrentIndexChanged: {
        console.debug(currentIndex)
      }
    }
  }
}