Cells in Spreadsheet are automatically underlined on second save or when the file is loaded dynamically.

Code to reproduce:
        string filePath = Server.MapPath("Test.xlsx");
        Telerik.Web.Spreadsheet.Workbook wkb = Telerik.Web.Spreadsheet.Workbook.Load(filePath);
        wkb.Save(filePath);

If you put a radspreadsheet inside a radtabstrip with multipage, the controls do not render properly.

In my scenario, I have a tabstrip embedded within a tabstrip, and a grid in the nested tabstrip.  That works fine.  Once you put a spreadsheet control in the multipage, the controls do not render properly. 

However, I was able to reproduce the results with the first scenario above, which is the most simple.

http://screencast.com/t/FJjlN3yw

The error message reads
'ContextMenus' could not be initialized. Details: Object reference on set to an instance of an object.

The SpreadProcessing library gets into account the current server culture and the SpreadsheetDocumentProvider uses different decimal and list separators based on the culture while the RadSpreadsheet control supports only comma as a list separator and dot as a decimal separator. 

The JavaScript error that is thrown when using the "sv-SE" culture is caused by the fact that this culture uses the comma as a decimal separator and semicolon as a list separator. 

One possible workaround is to change the current thread's culture before creating the Spreadsheet's provider and then restore the culture.

related to https://github.com/telerik/kendo-ui-core/issues/3519
workaround for rounding function is using Custom Functions http://docs.telerik.com/kendo-ui/controls/data-management/spreadsheet/custom-functions

kendo.spreadsheet.defineFunction("ROUND", function (x) {
    return Math.round(x);
}).args([
    ["x", "number"]
]);

Cell cell = new Cell() { Index = 0, Formula = "=ROUND(1.2)", Bold = true, Background = "#fef0cd", Format = "$0" };

The default font size on the client is not saved explicitly on the Excel file, so the Excel defaults take over (11px Calibri), so upon subsequent import all cells will have that font.

Steps to repro:

    go to https://demos.telerik.com/aspnet-ajax/spreadsheet/examples/import-export/defaultcs.aspx 
    export the file
    import the file

Expected: nothing changes

Actual: all cells are 11px Calibri
Workaround: Set a default font when the cell font is null
 
public override void SaveWorkbook(Workbook workbook)
{
    string path = "C:\\path-to-output.xlsx";
     
    for (int i = 0; i < workbook.Sheets.Count; i++)
    {
        for (int j = 0; j < workbook.Sheets[i].Rows.Count; j++)
        {
            for (int l = 0; l < workbook.Sheets[i].Rows[i].Cells.Count; l++)
            {
                string fontFamily = workbook.Sheets[i].Rows[i].Cells[l].FontFamily;
                workbook.Sheets[i].Rows[i].Cells[l].FontFamily = !string.IsNullOrEmpty(fontFamily) ? fontFamily : "Courier New";
 
                double? fontSize = workbook.Sheets[i].Rows[i].Cells[l].FontSize;
                workbook.Sheets[i].Rows[i].Cells[l].FontSize = fontSize.HasValue ? fontSize : 12;
            }
        }
    }
    workbook.Save(path);
}
 

In Internet Explorer version 11.418.18362.0, when hovering over the lower-right dot the cursor doesn't change to the expected cross-hair. 

To Reproduce:

1. Open IE11

2. Navigate to the ASP.NET Spreadsheet Demo

3. Highlight a few cells

4. Hover the cursor over the lower-right dot

Expected Behavior:

The cursor changes to a thin cross-hair icon but it doesn't change in IE 11.

Workaround: Placing the following script under the ScriptManager

<script>
        kendo.spreadsheet.registerEditor('_validation_list', function () {
            var context, list;
            function create() {
                var $list = $("[id$='SpreadsheetListBoxDropDown']").first();
                var element = $list.closest(".rssPopup");

                list = $find($list.attr("id"));
                if (!this._listdropdown) {
                    var dropdown = new kendo.spreadsheet.DropDown(element);
                    this._listdropdown = dropdown;

                    list.add_selectedIndexChanged(function (sender, args) {
                        dropdown.close();
                        var item = list.get_selectedItem();
                        if (item) {
                            context.callback(item.get_value());
                        }
                    });
                }

                this._listdropdown.openFor(context.view.element.find('.k-spreadsheet-editor-button'));
            }
            function open() {
                create();
                var matrix = context.validation.from.value;
                if (matrix) {

                    var items = list.get_items();
                    items.clear();
                    matrix.each(function (el) {
                        var item = new Telerik.Web.UI.RadListBoxItem();
                        item.set_text(el);
                        items.add(item);
                    });
                }
            }
            return {
                edit: function (options) {
                    context = options;
                    open();
                },
                icon: 'p-icon p-i-arrow-60-down'
            };
        });
    </script>

The issue is replicated when the spreadsheet is higher than the screen height. To reproduce it, scroll the page and click the last visible cell. 

Result: The page is scrolled to the beginning of the Spreadsheet element

Expected: The page is not scrolled

<telerik:RadSpreadsheet runat="server" ID="RadSpreadsheet1" Height="2000px" Width="100%">
</telerik:RadSpreadsheet>

Link is not clickable when situated in a disabled cell.

Steps to reproduce.

1. Place a link in a cell or a range of cells

2. Disable the cell (range)

3. Click the link

Expected: https://www.screencast.com/t/bvkiEnFk7uhc (as in the Kendo Spreadsheet http://demos.telerik.com/kendo-ui/spreadsheet/index)

Actual: https://www.screencast.com/t/6Vu2f1bR3Oy0 (the tooltip is not visible) https://demos.telerik.com/aspnet-ajax/spreadsheet/examples/overview/defaultcs.aspx

Workaround: 
Add the styles for the tooltip from the Kendo Spreadsheet

html body .RadSpreadsheet .k-tooltip {               

    border-radius: 4px;
    background-image: none, linear-gradient(rgba(255, 255, 255, 0.6) 0px, rgba(255, 255, 255, 0) 100%);
    background-color: rgb(234, 232, 232);
    color: rgb(49, 49, 49);
    box-shadow: rgba(0, 0, 0, 0.3) 0px 4px 6px;
    background-position: 50% 50%;
    border-color: transparent;
    z-index: 12000;
    min-width: 20px;
    text-align: center;
    border-style: solid;
    border-width: 0px;
    padding: 5px 5px 5px 6px;
    background-repeat: repeat-x;
}

When I load the radspreadsheet from an excel file, the foreground color is not loaded.

A workaround is to use the Kendo Spreadsheet widget directly which imports fore color: 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
    add some text with specific fore color
    save the excel file
    import the excel file

Expected: there is no change

Actual: the fore color is not imported. Also, font size changes, but see the related item for that