Workaround use the following code to programatically toggle the spell check mode: 

RadRibbonBarGroup spellCheckGroup = ((RibbonTab)richTextEditorRibbonBar1.CommandTabs[0]).Items[3] as RadRibbonBarGroup;
RadToggleButtonElement toggleButton = spellCheckGroup.Items[1] as RadToggleButtonElement;
if (this.radRichTextEditor1.IsSpellCheckingEnabled)
{
    toggleButton.CheckState = CheckState.Unchecked;
}
else
{
    toggleButton.CheckState = CheckState.Checked;
}

Due to a namespace conflict, projects which reference Telerik.WinControls.RichTextBox.dll and target .NET 4.5 or above, cannot be built successfully if they are using some of the conflicting types.
The conflict comes from the ICommand interface (https://msdn.microsoft.com/en-us/library/system.windows.input.icommand%28v=vs.110%29.aspx) which was moved from PresentationCore.dll to System.dll in .NET 4.5.

To reproduce:
- Export document with an inline UI elements to HTML.
- Import the document.

 Workaround:
- Manually export the UI elements information and then create new UI elements when the document is imported:
void ImportSettings_InlineUIContainerImporting(object sender, InlineUIContainerImportingEventArgs e)
{
    PropertyInfo property = typeof(InlineUIContainerImportingEventArgs).GetProperty("Handled");
    property.GetSetMethod(true).Invoke(e, new object[] { true });

    ObjectHandle handle = Activator.CreateInstance("Telerik.WinControls.UI", e.CommentContent);
    Object control = handle.Unwrap();
    InlineUIContainer container = new InlineUIContainer();
    RadElementUIContainer radContainer = new RadElementUIContainer(control as RadElement);
    container.UiElement = radContainer;
    container.Height = 30;
    container.Width = 300;
    e.TargetParagraph.Inlines.Add(container);
}
//export
private void btnWrite_Click(object sender, EventArgs e)
{
    HtmlFormatProvider provider = new HtmlFormatProvider();
    provider.ExportSettings.InlineUIContainerExporting += ExportSettings_InlineUIContainerExporting;         
  
    File.WriteAllText(Environment.GetFolderPath(Environment.SpecialFolder.Desktop) + "\\TelerikUITest.html", provider.Export(this.radRichTextEditor1.Document));
}

void ExportSettings_InlineUIContainerExporting(object sender, Telerik.WinForms.Documents.FormatProviders.Html.InlineUIContainerExportingEventArgs e)
{
    string control = ((RadElementUIContainer)e.InlineUIContainer.UiElement).Element.ToString();
    e.CommentContent = control;
}

Workaround: 
public class CustomRadRichTextEditor : RadRichTextEditor
{
    /// <summary>
    /// Gets or sets the width of the caret.
    /// </summary>
    [Browsable(false)]
    [Category(RadDesignCategory.AppearanceCategory)]
    public new float CaretWidth
    {
        get
        {
            float caretWidth = base.CaretWidth;
            if (float.IsNaN(caretWidth))
            {
                return 2;
            }

            return caretWidth;
        }
        set 
        { 
            base.CaretWidth = value; 
        }
    }
}

To reproduce:
- Click the AA Styles button to open the Styles dialog.
- Scroll down and select the CodeBlock item
- The style does not change


 

When the specified length of the stream is larger than the actual one, Adobe throws errors and removes the image.

Workaround:

Set the format provider settings:

PdfFormatProvider provider = new PdfFormatProvider();
PdfExportSettings exportSettings = new PdfExportSettings();
exportSettings.ContentsDeflaterCompressionLevel = 9;
exportSettings.ImagesDeflaterCompressionLevel = 9;
provider.ExportSettings = exportSettings;

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

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