The issue is reproducible when the style of the paragraph with the revisions is changed for the second time.

RadRichTextBox doesn't render a border that is not locally defined. In this case, the corresponding border from the applied table style should be used.

• Each RichText element should contain a unique id. The id contains DateTime.UtcNow.Ticks. This format is requiring to know which RT elements were added from the last change.
• Export these ids into html as is and import.
• For compatibility, id should have a different attribute name, for example:
  

  <p data-telerik-id="Paragraph637567542110611335">
  	<span data-telerik-id="Span637567542110611345">
  		Test
  	</span>
  </p>

  Note: data-* is Global attribute name: https://www.w3schools.com/tags/att_data-.asp
  
  Id value example:
  

  public class HiResDateTime
  {
  	private static long lastTimeStamp = DateTime.UtcNow.Ticks;
  	private static readonly Regex digitsOnly = new Regex(@"[^\d]");
  	public static long UtcNowTicks
  	{
  		get
  		{
  			long original, newValue;
  			do
  			{
  				original = lastTimeStamp;
  				long now = DateTime.UtcNow.Ticks;
  				newValue = Math.Max(now, original + 1);
  			} while (Interlocked.CompareExchange
  						 (ref lastTimeStamp, newValue, original) != original);
  
  			return newValue;
  		}
  	}
  
  	public static string UtcNowTicksString => digitsOnly.Replace(UtcNowTicks.ToString(), "");
  }

  
  

Currently, there is a DocumentHistory property IsEnabled indicating whether the history for the RadDocument is enabled. This property is not working and history cannot be disabled.

Workaround:

Use DocumentHistory Clear() method by attaching to editor's CommandExecuted event.

        private void Editor_CommandExecuted(object sender, Telerik.Windows.Documents.RichTextBoxCommands.CommandExecutedEventArgs e)
        {
            editor.Document.History.Clear();
        }

Add support for shapes, and especially for shapes with textual content. 
In OOXML, shapes are represented by the wps:wsp element, and shapes with textual content by <wps:txbx>, <w:txbxContent>.
Such shape can be added to a Word document using the Insert -> Text -> Text Box -> Draw Text Box, or through a shape's context menu -> Add Text.

Note: Do not confuse with Text/Rich Text content controls (https://feedback.telerik.com/Project/143/Feedback/Details/113730 ).

When the Track Changes is On and we try to change the style it applies the first time but the second try throws an exception and the style doesn't apply: System.ArgumentNullException: 'Value cannot be null. Parameter name: owner'.

1. Add new text "TEST".
2. Select the text and set a new style "Heading 2", then "Heading 1".
Observed: Heading 1 doesn`t appear.

When the Track Changes is activated, a Hyperlink is inserted to a text and we try to reject changes the rejection is not applied correctly.

The result:

When the unit type is set to an inch:

Expected: to could be able to place the RulerThumb on every 1/16 of an inch.
Actual: be able to place the RulerThumb to every 1/8 of an inch. 

The GetSupportedExtensions method of DocumentFormatProvidersManager throws NullReferenceException when invoked.

Workaround:

HashSet<string> supportedExtensions = new HashSet<string>();
foreach (var provider in DocumentFormatProvidersManager.FormatProviders)
{
    foreach (var extension in provider.SupportedExtensions)
    {
        supportedExtensions.Add(extension);
    }
}

When "rFonts" is set in docDefaults:

<w:styles>
	<w:docDefaults>
		<w:rPrDefault>
			<w:rPr>
				<w:rFonts w:ascii="Verdana" w:eastAsia="Times New Roman" w:hAnsi="Verdana" w:cs="Verdana"/>
				...
			</w:rPr>
		</w:rPrDefault>

and partially in the local run properties:

<w:r>
	<w:rPr>
		<w:rFonts w:cs="Times New Roman"/>
		...
	</w:rPr>
	<w:t>Text</w:t>
</w:r>

A wrong font is applied.

Expected: Verdana
Actual: Times New Roman

When inserting a content control (structured document tag) into an empty RadDocument using one of the overloads of the InsertStructuredDocumentTag method accessible from RadRichTextBox and RadDocumentEditor, a NullReferenceException is thrown.

Workaround: Invoke the EnsureDocumentMeasuredAndArranged method before inserting the content control:

document.EnsureDocumentMeasuredAndArranged();

RadDocumentEditor editor = new RadDocumentEditor(document);
editor.InsertStructuredDocumentTag(SdtType.CheckBox);