At the moment the print settings set to the WorksheetPageSetup class are not passed to the Print dialog which leads to bad user experience. If you set the print settings of the RadSpreadsheet like so:

WorksheetPageSetup pageSetup = this.radSpreadsheet.Workbook.ActiveWorksheet.WorksheetPageSetup;
pageSetup.PageOrientation = PageOrientation.Landscape;

and then select Print, the Spreadsheet print menu will show the print preview as landscape. However, when after that you click on Print for the default print dialog to appear and then click Preferences, you will notice that the preference is set to Portrait. The print job will be Landscape, but the incorrect information in the default dialog creates confusion.

This is an example of how to set the preference of the default dialog:

PrintDialog printDialog = new PrintDialog();
var printTicket = printDialog.PrintTicket;
printTicket.PageOrientation = System.Printing.PageOrientation.Landscape;

The fix will be available in our next LIB release (v. 2015.03.1005).

The BitmapImage class throws the exception. We could show some kind of no-image-placeholder instead of throwing exception, or skip the image.

Telerik Reporting creates such files.

Attached is a sample project demonstrating how to customize the Open command descriptor to remove .emf images just after importing the document.

Available in R3 2018 Official Release Version.

The data validation error message box has an invalid size when shown multiple times

The fix will be available in our latest LIB release (v. 2015.02.0803).

When importing a document containing a destination that does not refer to a formula an exception is thrown: System.NullReferenceException: 'Object reference not set to an instance of an object.'

The fix is available in our latest LIB release (v.2015.3.1026). 

If a document contains many and complex formulas (with many functions having other functions as arguments) it may take a long time to show in the control.

Some documents with conditional formatting occasionally throw an ArgumentOutOfRangeException due to an internal issue with dfsx indexing.

The style gallery is broken in the fluent theme and crashes the control

The SpreadsheetML format has built-in reserved names. When such a name is defined in the scope of a worksheet, a SpreadsheetNameException is thrown during parsing the document.

If you set, for example, two copies, the printed copies will be 4. If you select three copies, the result will be nine copies.

The problem is that the spreadsheet wants to identify the main window. The main window is not known to the plugin and should not be, because it is located in a different app domain due to the specifics of the architecture (https://docs.microsoft.com/en-us/archive/msdn-magazine/2014/january/wpf-build-fault-tolerant-composite-applications).

Add sheet button is hidden when there are many sheets. This should be checked with all themes.

When a cell that has a defined name is selected, the associated name should appear in the name box. However, when the cell is part of a merged range, its row and column name (A1) is shown instead of the defined name.

NullReferenceException when importing a scatter chart with only one axis 

When attaching to the CellPropertyChanged event and trying to modify the cell an exception is thrown:

if firstly detached from the event and then modify the cell the exception is: 
System.InvalidOperationException: 'Collection was modified; enumeration operation may not execute.' 

else:
System.StackOverflowException: 'Exception of type 'System.StackOverflowException' was thrown.'

When importing a document containing a ChartSheet (currently not supported: Implement support for ChartSheet) with a smaller tab index than the WorkSheet an ArgumentOutOfRangeException is thrown.

When the users copy an image and paste it to another RadSpreadsheet, then export the Workbook to XLSX, the generated document contains invalid relation as the image is not properly registered inside the resources of the workbook.