Vega Barchart autosize fit-x grid problem

vegaspec.json

{
  "width": 500,
  "autosize": {
    "type": "fit-x",
    "contains": "padding"
  },
  "signals": [
    {
      "name": "barWidth",
      "value": 24
    },
    {
      "name": "groupHeight",
      "update": "(barWidth * 3)"
    }
  ],
  "data": [
    {
      "name": "table",
      "values": [
        {
          "xValue": "A",
          "xIndex": 0,
          "yValue": 4691,
          "cValue": 0
        },
        {
          "xValue": "A",
          "xIndex": 0,
          "yValue": 4212,
          "cValue": 1
        },
        {
          "xValue": "A",
          "xIndex": 0,
          "yValue": 7097,
          "cValue": 2
        },
        {
          "xValue": "B",
          "xIndex": 1,
          "yValue": 1810,
          "cValue": 0
        },
        {
          "xValue": "B",
          "xIndex": 1,
          "yValue": 7037,
          "cValue": 1
        },
        {
          "xValue": "B",
          "xIndex": 1,
          "yValue": 4239,
          "cValue": 2
        }
      ]
    }
  ],
  "scales": [
    {
      "name": "xScale",
      "type": "linear",
      "range": "width",
      "domain": {
        "data": "table",
        "field": "yValue"
      },
      "nice": true,
      "zero": true
    },
    {
      "name": "yScale",
      "type": "band",
      "range": {
        "step": {
          "signal": "groupHeight"
        }
      },
      "domain": {
        "data": "table",
        "field": "xValue"
      },
      "paddingInner": 0.1,
      "paddingOuter": 0
    },
    {
      "name": "colorScale",
      "type": "ordinal",
      "range": "category",
      "domain": {
        "data": "table",
        "field": "cValue"
      }
    }
  ],
  "marks": [
    {
      "type": "group",
      "name": "blocks",
      "from": {
        "facet": {
          "name": "series",
          "data": "table",
          "groupby": "xValue"
        }
      },
      "encode": {
        "enter": {
          "y": {
            "signal": "scale('yScale', datum.xValue)"
          },
          "x": {
            "value": 0
          },
          "width": {
            "value": 20
          },
          "height": {
            "signal": "bandwidth('yScale')"
          }
        }
      },
      "signals": [
        {
          "name": "height",
          "update": "bandwidth('yScale')"
        }
      ],
      "marks": [
        {
          "type": "group",
          "encode": {
            "enter": {
              "y": {
                "value": 0
              },
              "x": {
                "value": 0
              },
              "width": {
                "signal": "width"
              },
              "height": {
                "signal": "height"
              }
            }
          },
          "scales": [
            {
              "name": "barPositionBand",
              "type": "band",
              "range": "height",
              "domain": {
                "data": "series",
                "field": "cValue"
              },
              "paddingInner": 0.1,
              "paddingOuter": 0
            }
          ],
          "data": [
            {
              "name": "xValues",
              "source": "series",
              "transform": [
                {
                  "type": "aggregate",
                  "groupby": [
                    "xValue"
                  ]
                }
              ]
            }
          ],
          "marks": [
            {
              "type": "rect",
              "name": "bar",
              "from": {
                "data": "series"
              },
              "encode": {
                "enter": {
                  "y": {
                    "scale": "barPositionBand",
                    "field": "cValue"
                  },
                  "height": {
                    "signal": "bandwidth('barPositionBand')"
                  },
                  "x": {
                    "scale": "xScale",
                    "field": "yValue"
                  },
                  "x2": {
                    "value": 0
                  },
                  "fill": {
                    "scale": "colorScale",
                    "field": "cValue"
                  }
                }
              }
            }
          ]
        }
      ]
    }
  ],
  "axes": [
    {
      "orient": "top",
      "scale": "xScale",
      "domain": false,
      "grid": true,
      "ticks": true
    },
    {
      "orient": "left",
      "scale": "yScale",
      "domain": true,
      "grid": false,
      "labels": true,
      "ticks": false
    }
  ]
}