Unexpected offset of boxplots when filtering aggregated temporal data

[jwoLondon]

Using the Boxplot mark when aggregating and filtering temporal data produces an unexpected chart offset that varies depending on how far after 1970 values are filtered out. In the example below try changing 1985 to a later or earlier year.

The fact this only occurs beyond 1970 suggests there may be a time parsing issue somewhere. If the mark is changed to a primitive such as circle, there is no offset.

{
  "$schema": "https://vega.github.io/schema/vega-lite/v3.json",
  "width": 600,
  "data": {
    "url": "https://gicentre.github.io/data/temperatureAnomalies.json",
    "format": {"parse": {"Anomaly": "number"}}
  },
  "transform": [{"filter": "year(datum.Date) >= 1985"}],
  "encoding": {
    "x": {
      "field": "Date",
      "type": "temporal",
      "timeUnit": "year"
    },
    "y": {"field": "Anomaly", "type": "quantitative"}
  },
  "mark": "boxplot"
}

[kanitw]

Related issue: Try changing temporal to ordinal breaks the chart entirely:

{
  "$schema": "https://vega.github.io/schema/vega-lite/v3.json",
  "width": 600,
  "data": {
    "url": "https://gicentre.github.io/data/temperatureAnomalies.json",
    "format": {"parse": {"Anomaly": "number"}}
  },
  "transform": [{"filter": "year(datum.Date) >= 1985"}],
  "encoding": {
    "x": {
      "field": "Date",
      "type": "ordinal",
      "timeUnit": "year"
    },
    "y": {"field": "Anomaly", "type": "quantitative"}
  },
  "mark": "boxplot"
}