The button should always be active. 

The button:

When the Freeze Panes option is enabled and try to insert a new comment into the next cell on the left to the Freeze Panes separator the comment is deleted.

Fill right shortcut (Ctrl + R) does not work 

As a workaround, manually register the combination:

public MainWindow()
{
    InitializeComponent();
    this.radSpreadsheet.ActiveSheetChanged += RadSpreadsheet_ActiveSheetChanged;
    
    this.Loaded += MainWindow_Loaded;
}

private void MainWindow_Loaded(object sender, RoutedEventArgs e)
{
    RegisterFillRight();
}

private void RadSpreadsheet_ActiveSheetChanged(object sender, EventArgs e)
{
    RegisterFillRight();
}
public void RegisterFillRight()
{
    RadWorksheetEditor worksheetEditor = this.radSpreadsheet.ActiveWorksheetEditor;

    if (this.radSpreadsheet.ActiveWorksheetEditor != null)
    {
        worksheetEditor.KeyBindings.RegisterCommand(worksheetEditor.Commands.FillRight, Key.R, ModifierKeys.Control);
    }
}

There are several items that currently cannot be localized:

• Fit Sheet on One page
• Fit All Columns on One page
• Fit All Rows on One page

The headers and the description of the items have hardcoded strings.

When importing a document containing a hyperlink formula (e.g. "=HYPERLINK(B2,A2)") an exception is thrown: System.Collections.Generic.KeyNotFoundException: 'The given key was not present in the dictionary.'

The WorkbookContentChanged event is invoked right after importing a document. 

The scale factor is not imported from documents with no information about the selection state.