A workaround is using directly the Kendo Spreadsheet widget as this will allow you to use its latest version that does not manifest this issue: https://demos.telerik.com/kendo-ui/spreadsheet/server-side-import-export

Repro steps

    Go to https://demos.telerik.com/aspnet-ajax/spreadsheet/examples/import-export/defaultcs.aspx
    Go to an empty cell
    type some text
    change its font size (e.g., to 18)
    save the file
    import the file you just saved

Expected: nothing changes

Actual: (some) cells change their height and font size, not just the cell that was edited above