Workaround: Set the next style property for all types except the Paragraph to an empty string
foreach (var style in this.radRichTextBox.Document.StyleRepository)
{
    if (style.Type!=Telerik.Windows.Documents.Model.Styles.StyleType.Paragraph && !string.IsNullOrEmpty(style.NextStyleName))
    {
        style.NextStyleName = string.Empty;
    }
}

To reproduce:
 - Add a table where the width is set to 100%
 - Import the table and the export it:
private void radButton_Click(object sender, RoutedEventArgs e)
{
    var provider = new HtmlFormatProvider();
    string text = File.ReadAllText(@"..\..\default.html");
    rtb1.Document = provider.Import(text);
}

private void radButton1_Click(object sender, RoutedEventArgs e)
{
    var provider = new HtmlFormatProvider();
    provider.ExportSettings.StylesExportMode = StylesExportMode.Inline;
    string content = provider.Export(rtb1.Document);
    File.WriteAllText(@"D:\test1.html", content);
}

Workaround:
 Leave the export mode intact.

How to reproduce: create a document like the one below, then try to add a comment  for an element in the paragraph with the bookmarks
Public Class Form2
    Sub New()

        InitializeComponent()

        Dim document As New RadDocument()
        Dim section As New Section()
        Dim paragraph As New Paragraph()
        Dim span As New Span("Content prior range[")
        Dim span2 As New Span("]Content after range")
        Dim readOnlyContent As New Span("READ ONLY")
        Dim rangeStart As New ReadOnlyRangeStart()
        Dim rangeEnd As New ReadOnlyRangeEnd()
        rangeEnd.PairWithStart(rangeStart)
        paragraph.Inlines.Add(span)
        paragraph.Inlines.Add(rangeStart)
        paragraph.Inlines.Add(readOnlyContent)
        paragraph.Inlines.Add(rangeEnd)
        paragraph.Inlines.Add(span2)
        section.Blocks.Add(paragraph)
        document.Sections.Add(section)

        Dim bmSection As New Section()
        Dim bmParagraph As New Paragraph()
        Dim bmSpan As New Span("Content prior bookmark[")
        Dim bmSpan2 As New Span("]Content after bookmark")
        Dim bmContent As New Span("Content in Bookmark")
        Dim bmRangeEnd As New BookmarkRangeEnd()
        Dim bmRangeStart = DirectCast(bmRangeEnd.CreatePairedStart(), BookmarkRangeStart)
        bmRangeStart.Name = System.Guid.NewGuid().ToString()
        bmParagraph.Inlines.Add(bmSpan)
        bmParagraph.Inlines.Add(bmRangeStart)
        bmParagraph.Inlines.Add(bmContent)
        bmParagraph.Inlines.Add(bmRangeEnd)
        bmParagraph.Inlines.Add(bmSpan2)
        bmSection.Blocks.Add(bmParagraph)
        document.Sections.Add(bmSection)

        Me.RadRichTextEditor1.Document = document

    End Sub
End Class

Steps to reproduce: 
1. Use the following code snippet: 
public partial class Form1 : RadForm
{
    public Form1()
    {
        InitializeComponent();
        this.WindowState = System.Windows.Forms.FormWindowState.Maximized;
    
        this.radRichTextEditor1.Document = ImportDocx(@"..\..\lorem.docx");
        this.radRichTextEditor1.LayoutMode = DocumentLayoutMode.Paged;
        this.radRichTextEditor1.ChangeSectionPageSize(PaperTypeConverter.ToSize(PaperTypes.A3));
        this.radRichTextEditor1.ChangeSectionPageOrientation(PageOrientation.Landscape);
    }

    private void radButton1_Click_1(object sender, EventArgs e)
    {
        this.radRichTextEditor1.PrintPreview();
    }

    private void radButton3_Click(object sender, EventArgs e)
    {
        this.radRichTextEditor1.Print(true);
    }	
}

Calling the PrintPreview method, the page orientation is updated in PrintSettingDialog. However, the page size is not updated correctly. As result, the printed document is not correct. 
If you call the Print method, the page size and orientation are not updated and the document is printed as in A4/Portrait instead A3/Landscape. 

Workaround:
Use RadPrintDocument: 
private void radButton2_Click(object sender, EventArgs e)
{
    RadPrintDocument radPrintDocument1 = new RadPrintDocument();         
    radPrintDocument1.AssociatedObject = this.radRichTextEditor1;
    radPrintDocument1.Landscape = true;
    PaperSize ps = new PaperSize();
    ps.RawKind = (int)PaperKind.A3;
    radPrintDocument1.DefaultPageSettings.PaperSize = ps;
    radPrintDocument1.Print();
    //this.radRichTextEditor1.Print(true, radPrintDocument1);
}

To reproduce: add some text to RadRichTextEditor and set the Enabled property to false. You will notice that the text gets bold and blurry. 

Workaround: instead of disabling RadRichTextEditor, use the ReadOnly property.

The RTF specifications states that the header of the document should start with "\rtfN" where N is the version of the RTF. Currently, the RtfFormatProvider do not save the version, but only "\rtf". Most software handles this case, but in some cases the document cannot be read.

How to reproduce:
1. Run the Mail Merge example (QSF) 

2. Select the image inside the document and move it to another position

To reproduce: please refer to the attached gif file

Add a custom tab in the ribbon UI and a RadDropDownListElement bound to a list of strings. The first item is selected by default. Insert a table by using the ribbon UI and try to get programmatically the RadDropDownListElement.SelectedValue/Index. It is null/-1 although the text is correct.

Workaround:

public class CustomRichTextEditorRibbonBar : RichTextEditorRibbonBar
{
           protected override void CreateChildItems(RadElement parent)
    {
        base.CreateChildItems(parent);
        FieldInfo fi = typeof(RadRibbonBar).GetField("ribbonBarElement", BindingFlags.Instance | BindingFlags.NonPublic);
        RadRibbonBarElement ribbonBarElement = fi.GetValue(this) as RadRibbonBarElement;

        ribbonBarElement = new CustomRadRibbonBarElement();
        fi.SetValue(this, ribbonBarElement);
        this.RootElement.Children.Add(ribbonBarElement);

        ribbonBarElement.CommandTabSelecting +=
            delegate (object sender, CommandTabSelectingEventArgs args) { OnCommandTabSelecting(args); };
        ribbonBarElement.CommandTabSelected +=
            delegate (object sender, CommandTabEventArgs args) { OnCommandTabSelected(args); };

        ribbonBarElement.ExpandedStateChanged += delegate (object sender, EventArgs args)
        {
            this.OnRibbonBarExpandedStateChanged(args);
        };


    }
}

public class CustomRadRibbonBarElement : RadRibbonBarElement
{
  
    protected override float GetMaximumTabContentHeight()
    {
        return 104; 
    }
}

How to reproduce:
private void radButton1_Click(object sender, EventArgs e)
{
    RadPrintDocument doc = new RadPrintDocument();
    doc.Margins = new Margins(0, 0, 10, 10);

    doc.AssociatedObject = this.radRichTextEditor1;
    RadPrintPreviewDialog dialog = new RadPrintPreviewDialog();
    dialog.Document = doc;
    dialog.ShowDialog();
}

Workaround: apply the margins on the document loaded in the editor
private void radButton1_Click(object sender, EventArgs e)
{
    RadPrintDocument doc = new RadPrintDocument();
    this.radRichTextEditor1.Document.SectionDefaultPageMargin = new Telerik.WinForms.Documents.Layout.Padding(0, 0, 10, 10);

    doc.AssociatedObject = this.radRichTextEditor1;
    RadPrintPreviewDialog dialog = new RadPrintPreviewDialog();
    dialog.Document = doc;
    dialog.ShowDialog();
}

InvalidOperationException is thrown in the IsInNonEditableRange() method of RadDocument when assigning a document to RadRichTextBox, which is created through the model and contains several read-only ranges.

Workaround: Call MeasureAndArrangeInDefaulSize().

When exporting to HTML, each two consequent spaces in a run are treated as  . However, when a style is applied to one of the spaces, the span is split and the two spaces are not considered as a pair, therefore, the HtmlFormatProvider exports them as normal spaces.

When the two spaces are the whole content of a paragraph, this paragraph is not visible when the HTML is visualized in a browser. 

To reproduce:

1. Add a RichTextEditorRibbonBar on the form
2. Add a RadRichTextEditor on the form.
3. Set the RichTextEditorRibbonBar.AssociatedRichTextEditor property.
4. Run the application. You will notice that the caret for the RadRichTextEditor is displayed and the user expects to start entering text when pressing the keyboard. However,  the focused control in this case is the font family drop-down and it accepts the input. 

Workaround: focus the RadRichTextEditor in the Form.Shown event:

Private Sub Form1_Shown(sender As Object, e As EventArgs) Handles MyBase.Shown
    Me.RadRichTextEditor1.Focus()
End Sub

To reproduce:
- Set the layout to Paged.
- Add a table
- Switch the layout to Flow and try to resize it on the right most border.

Workaround:
Switch to paged layout and resize the table.