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).

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 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.

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

The user needs to either double click or hit F2 in order to proceed.

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

With the current implementation, the Notes support only a rectangular shape.

Examples:

The cursor position is changed when one clicks in the middle of a formula. The cursor is moved to the end of the text. 

Fill down (Ctrl-D) is not working in a protected worksheet with an unlocked range of cells.

NullReferenceException when the document contains paragraph elements with no text. 

telerik:Label's Context is set to itself and is throwing an error while searching for a not existing 'Title' property within itself.

The sheet navigation does not work with specific theme and document.

Searching with Ctrl-F in a sheet with many rows takes a long time.

InvalidOperationException (Sequence contains no matching element) when editing a note.

Investigate if the performance with large files can be improved. Currently a document with a million ros is opened slowly and the memory consumption is high. 

Copy/Paste a shape and then an image leads to a wrong result. 

Steps to reproduce: 

1. Copy plain text from a plain text editor onto the clipboard -> Paste in Spreadsheet and the text is pasted OK.
2. Copy the image from another app onto the clipboard -> Paste in Spreadsheet and the "This information cannot be pasted" dialog is displayed.
3. Insert picture from file into spreadsheet -> image displayed in a shape.
4. Select and copy the shape.
5. Repeat step 1 => Copy plain text from a plain text editor onto the clipboard -> Paste in Spreadsheet and the text is pasted OK.
6. Repeat step 2 => Copy image from another app onto clipboard -> Paste in Spreadsheet and shape selected and copied in step 4 is pasted. => Not expected result.

Spreadsheet: Add the ability to build formulas using keyboard navigation:

1. Press '=' in a cell. The cell goes into Edit Mode. 
2. Use the Keyboard arrow keys to move in any direction. The Cell reference of the focused cell is automatically entered after the '=' into the cell which is in edit mode.
3. The user can press the Control+Arrow Key to add a reference to an entire row or column of data.

For the German language translations, the following resource keys are translated into Dutch instead:

• Spreadsheet_PrintPreview_FitSheetOnOnePage
• Spreadsheet_PrintPreview_FitSheetOnOnePage_Description
• Spreadsheet_PrintPreview_FitColumnsOnOnePage
• Spreadsheet_PrintPreview_FitColumnsOnOnePage_Description
• Spreadsheet_PrintPreview_FitRowsOnOnePage
• Spreadsheet_PrintPreview_FitRowsOnOnePage_Description

#.##0,00;-#.##0,00;;@ does not work in RadSpreadsheet. It should suppress visualizing of ) values.

Workaround: #.##0,00;-#.##0,00; ;@ works fine (there is ' ' [space] set for the zero values).