Misaligned table rows with `fixed_row` / `fixed_column` after mousing over table

[michaelbabyn]

This looks like the same error as #777 only it doesn't appear until I mouse back over the table after scrolling. Originally reported in the community

Code:

import dash
import dash_table
import pandas as pd

df = pd.read_csv('https://raw.githubusercontent.com/plotly/datasets/master/solar.csv')

app = dash.Dash(__name__)

app.layout = dash_table.DataTable(
    columns=[{"name": i, "id": i} for i in list(df.columns) * 3],
    data=df.to_dict('records'),
    fixed_rows={'headers': True},
    style_cell={'minWidth': '180px', 'width': '180px', 'maxWidth': '180px'},
)

if __name__ == '__main__':
    app.run_server(debug=True, port=8022)

[chriddyp]

Another report by a community user: https://community.plotly.com/t/dash-1-12-datatable-format-issues-when-using-fixed-header/39120/15?u=chriddyp

[chriddyp]

cc @plotly/dash-core