split_by doesn't respect the date formatting settings

[vera-atomic]

Bug Report

When formatting dates, configurations don't apply when the column is used as split_by

Steps to Reproduce:

take the datagrid example on perspective's main page:

I formatted the lastUpdate column in a custom way with this config:

"lastUpdate": {
      "date_format": {
        "format": "custom",
        "second": "disabled",
        "minute": "disabled",
        "hour": "disabled"
      }
    }

It works, the lastUpdate column does not show the times only the date.
Now if I try to use the lastUpdate column as a split_by, it doesn't respect that formatting and displays the times once more:

Expected Result:

I expect the formatting to apply in all situations, regardless of where I'm using the column

Actual Result:

Now if I try to use the lastUpdate column as a split_by, it doesn't respect that formatting and displays the times once more

Environment:

Perspective main page, viewed on Chrome