To reproduce:
- Click the InsertMergeFiled button before setting the data source.
- Set the data source.
- Click the button again.
- There are no items in it.
 

Workaround:
Friend Class MyRichTextEditorRibbonBar
    Inherits RichTextEditorRibbonBar



    Protected Overrides Sub dropDownButtonInsertMergeField_DropDownOpening(sender As Object, e As CancelEventArgs)
        MyBase.dropDownButtonInsertMergeField_DropDownOpening(sender, e)
        If Me.dropDownButtonInsertMergeField.Items.Count = 0 Then
            Me.dropDownButtonInsertMergeField.Items.Add(New RadItem)
        End If
    End Sub

End Class

"http://" prefix is automatically added by the Insert Hyperlink Dialog when the provided URI is to local path or mapped drive, e.g. "Z:\temp".

Workaround 1: Set HyperlinkPattern to something that matches file paths, e.g.:
(this.radRichTextEditor1.RichTextBoxElement.InsertHyperlinkDialog as InsertHyperlinkDialog).HyperlinkPattern = ".*";

Workaround 2: Insert such paths with the "file://" prefix.

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().

This field retrieves a character through a code value specified in the field-argument. Such documents are common and are created when symbols (e.g. with font Windings through Insert -> Symbol dialog) are inserted in RTF documents in MS Word.

- There should be a formatting symbol for the character

- Pressing Ctrl+Shift+Space should insert the character (standard MS Word shortcut)

- Import from docx should be implemented

- The symbol should be treated as a separator between words when spell-checking

The attached video shows how you can reproduce this.

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.

Currently all tables are stuck to the let and there cannot be a text before them.

To reproduce: 
Please refer to the attached sample application and video demonstrating the experience issue. 

Workaround: 
Set RadRichTextEditor to null in Form`s Dispose method: 
Protected Overrides Sub Dispose(ByVal disposing As Boolean)
    Me.RadRichTextEditor1 = Nothing
    Try
        If disposing AndAlso components IsNot Nothing Then
            components.Dispose()
        End If
    Finally
        MyBase.Dispose(disposing)
    End Try
End Sub

Workaround: use a custom RichTextEditorRibbonBar

Public Class CustomRichTextEditorRibbonBar
Inherits RichTextEditorRibbonBar

    Dim headerText As String
    Protected Overrides Function GetInsertTableItems() As RadItemCollection
        Dim collection As RadItemCollection = MyBase.GetInsertTableItems()
        Dim headerItem As RadMenuInsertTableItem = TryCast(collection(0), RadMenuInsertTableItem)
        headerText = "My Header Text"
        Dim fi As FieldInfo = GetType(RadMenuInsertTableItem).GetField("header", BindingFlags.NonPublic Or BindingFlags.Instance)
        Dim header As LightVisualElement = fi.GetValue(headerItem)
        header.Text = headerText
        AddHandler header.TextChanged, AddressOf header_TextChanged
        Return collection
    End Function

    Private Sub header_TextChanged(sender As Object, e As EventArgs)
        Dim lve As LightVisualElement = TryCast(sender, LightVisualElement)
        If lve.Text = "Insert Table" Then
            lve.Text = headerText
        End If
    End Sub
End Class

Please refer to the attached screenshot. It is not possible to localize the marked label.

Workaround:

 Sub New()
     InitializeComponent() 
     Me.RadRichTextEditor1.RichTextBoxElement.InsertHyperlinkDialog = New CustomInsertHyperlinkDialog()
 End Sub

 Public Class CustomInsertHyperlinkDialog
     Inherits InsertHyperlinkDialog
     Protected Overrides Sub OnLoad(e As EventArgs)
         MyBase.OnLoad(e)
         Me.Controls("radLabel4").Text = "My address"
     End Sub
 End Class

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 (http://feedback.telerik.com/Project/154/Feedback/Details/156478 )