Config attribute of dcc.Graph does not respond to callbacks (is read-only)

When using a callback to control the modebar settings on a chart through the config property of a dcc.Graph, the graph does not update but retains the initial setting.

Note: I have not (yet) tested with other config settings.

Minimal example

import dash
import dash_core_components as dcc
import dash_html_components as html
from dash.dependencies import Input, Output, State
import plotly.express as px

app = dash.Dash()
server = app.server

app.layout = html.Div(
    [
        dcc.Graph(
            id="line-graph",
            figure=px.line(x=[1, 2, 3], y=[1, 2, 3]),
        ),
        dcc.RadioItems(
            options=[
                {"label": "Show modebar", "value": 1},
                {"label": "Hide modebar", "value": 0},
            ],
            value=1, # Note that if this value is set to 0 then the modebar will stay turned off rather than turned on.
            id="radio",
        ),
        html.Div([html.H3("Current config"), html.P(id="cur-config")]),
    ]
)


@app.callback(
    [Output("line-graph", "config"), Output("cur-config", "children")],
    [Input("radio", "value")],
)
def toggle_modebar(i):
    vals = [False, True]
    config = {"displayModeBar": vals[i]}
    return config, str(config)


if __name__ == "__main__":
    app.run_server(debug=True, port=8050)

Screen recording

https://user-images.githubusercontent.com/38958867/107691811-edb77d00-6c79-11eb-8488-c750b635f815.mov

Start by running the minimal Python example and exercising the dcc.Graph config callback with the modebar setting. Trace how dcc.Graph receives and applies callback updates, then verify that changing the radio selection changes the graph's modebar behavior rather than only the displayed config.