Replacing a GridLayout cell with a repeater complains

QGridLayoutEngine::addItem: Cell (0, 0) already taken
QGridLayoutEngine::addItem: Cell (0, 0) already taken
QGridLayoutEngine::addItem: Cell (0, 1) already taken
QGridLayoutEngine::addItem: Cell (0, 1) already taken

import QtQuick 2.7
import QtQuick.Controls 1.4
import QtQuick.Layouts 1.3 as Layouts

Item {
    id: base
    property var categories: ['one', 'two', 'three']
    property var values: [1, 2, 3]
    width: 800
    height: 600

    Column {
      Button {
        text: "Cause error output"
        onClicked: {
          base.categories = ['eleven', 'twelve']
          base.values = [11, 12]
        }
      }
      Button {
        text: "DOES NOT Cause error output"
        onClicked: {
          base.categories = ['eleven']
          base.values = [11]
        }
      }
    }

    Layouts.GridLayout {
      anchors.fill: parent
      columns: 2

      // CATEGORY LABELS...
      Repeater {
          model: base.categories // modelData will be the categories
          Item {
              Layouts.Layout.row: index
              Layouts.Layout.column: 0
              Layouts.Layout.preferredWidth: _categoryLabel.width
              Layouts.Layout.fillHeight: true
              // The actual category label...
              Text {
                  id: _categoryLabel
                  height: parent.height
                  anchors.right: parent.right
                  text: modelData
                  verticalAlignment: Text.AlignVCenter
                  font.pointSize: 27
                  leftPadding: 10
              }
          }
      }

      Repeater {
          model: base.values // modelData will be the values
          Item {
              Layouts.Layout.row: index
              Layouts.Layout.column: 1
              Layouts.Layout.preferredWidth: _categoryLabel.width
              Layouts.Layout.fillHeight: true
              // The actual value label...
              Text {
                  id: _categoryLabel
                  height: parent.height
                  anchors.right: parent.right
                  text: modelData
                  verticalAlignment: Text.AlignVCenter
                  font.pointSize: 27
                  leftPadding: 10
              }
          }
      }
  }
}