To reproduce:

- Select several words by holding the control key. 

- Paste some text. 

Result: the first word is replaced, the other are deleted

Expected: the text should be pasted in all selected places

Workaround:

private void RadRichTextBox_CommandExecuting(object sender, Telerik.Windows.Documents.RichTextBoxCommands.CommandExecutingEventArgs e)
{
    if (e.Command is PasteCommand)
    {
        var ranges = radRichTextBox.Document.Selection.Ranges.ToList();
        if (ranges.Count > 1)
        {
            e.Cancel = true;

            foreach (var range in ranges)
            {
                radRichTextBox.Document.Selection.Clear();
                radRichTextBox.Document.Selection.AddSelectionStart(range.StartPosition);
                radRichTextBox.Document.Selection.AddSelectionEnd(range.EndPosition);
                PasteNewText();
            }      
        }
    }
}
public void PasteNewText()
{
    DocumentFragment clipboardDocument = null;
    string clipboardText = null;
    bool clipboardContainsData = false;

    if (ClipboardEx.ContainsText(null))
    {
        clipboardText = ClipboardEx.GetText(null);
        clipboardContainsData = true;
    }

    if (!clipboardContainsData)
    {
        return;
    }

    if (clipboardDocument != null)
    {
        this.radRichTextBox.ActiveDocumentEditor.InsertFragment(clipboardDocument);
    }
    else if (!string.IsNullOrEmpty(clipboardText))
    {
        this.radRichTextBox.ActiveDocumentEditor.Insert(clipboardText);
    }
}