vega-lite: Columns not working properly in VL spec (possibly period in name of column?)

Have not seen this behavior before. I am trying to make columns from a field with a period in its name; I’ve done this successfully for other fields before, so maybe that’s the culprit? Anyway, column has "field: [gpuinfo.name]" and I have two values for gpuinfo.name, both of which appear in the final plot but all data points, no matter which GPU I choose, are in the same column.

I sincerely hope I just didn’t botch my specification somewhere. (This was generated from Altair.)

{
  "mark": "point",
  "data": {
    "values": [
      {
        "engine": "Gunrock",
        "algorithm": "BFS",
        "num_gpus": 1,
        "elapsed": 43.28049087524414,
        "dataset": "soc-LiveJournal1",
        "m_teps": 1563.7744140625,
        "gpuinfo.name": "GPU 1"
      },
      {
        "engine": "Gunrock",
        "algorithm": "BFS",
        "num_gpus": 2,
        "elapsed": 43.28049087524414,
        "dataset": "soc-LiveJournal1",
        "m_teps": 3456.7,
        "gpuinfo.name": "GPU 1"
      },
      {
        "engine": "Gunrock",
        "algorithm": "CC",
        "num_gpus": 1,
        "elapsed": 31.613856554031372,
        "dataset": "soc-LiveJournal1",
        "m_teps": 2710.914794921875,
        "gpuinfo.name": "GPU 2"
      }
    ]
  },
  "encoding": {
    "color": {
      "field": "engine",
      "type": "nominal",
      "legend": {"title": "Engine"}
    },
    "column": {
      "field": "[gpuinfo.name]",
      "type": "nominal",
      "axis": {"orient": "top","title": "GPU"}
    },
    "shape": {
      "field": "engine",
      "type": "nominal",
      "legend": {"title": "Engine"}
    },
    "y": {
      "field": "m_teps",
      "scale": {"type": "log"},
      "type": "quantitative",
      "axis": {"title": "MTEPS"}
    },
    "x": {
      "field": "num_gpus",
      "type": "nominal",
      "axis": {"title": "Number of GPUs"}
    },
    "row": {
      "field": "algorithm",
      "type": "nominal",
      "axis": {"title": "Primitive"}
    }
  }
}