Tooltip doesn't appear in layered chart when one layer has scale-bound selection

[jakevdp]

Reproduction (vega editor):

{
  "config" : {"circle": {"tooltip": true, "size": 300}},
  "encoding": {
    "x": {"type": "quantitative", "field": "x"},
    "y": {"type": "quantitative", "field": "y"}
  },
  "layer": [
    {
      "data": {"values": [{"x": 0, "y": 1.5}]},
      "mark": {"type": "circle", "color": "red"}
    },
    {
      "data": {"values": [{"x": 0, "y": 0.1}]},
      "mark": {"type": "circle", "color": "black"},
      "selection": {"sel": {"type": "interval", "bind": "scales"}}
    }
  ]
}

The tooltip is visible when hovering over the black point, and not visible over the red point. The tooltip appears correctly if both layers have a selection or if neither layer has a selection.

[ihightower]

a temporary work around in python is it to add "interactive" to charts separately.

this bug was reported by jakevdp (based on below stackoverflow post) and the temporary workaround is to follow the comment and the answer shown by ihightower).

https://stackoverflow.com/questions/59671294/altair-unable-to-get-tooltips-for-one-layer-in-a-line-chart/

[fxwiegand]

It should be mentioned that other plots added with concat are also affected by the problem as explained in #6773. This can be seen in this example.