When the variation is changed in the VisualStudio2013 theme, the Foreground is not updated. 

As a workaround, you can reset the Template of the control:

var template = this.syntaxEditor.Template;
this.syntaxEditor.Template = null;
this.syntaxEditor.Template = template;

Character data sections are not recognized and colored by the XmlTagger in SyntaxEditor.

Visual Studio:

SyntaxEditor:

Also parsing such elements is wrong:

Expanded OK:

Collapsed BUG (Node is closed but it shouldnt):

issue 2 - single line CDATA does not need folding button

//using System;

//usign System.Windows.Controls;

Two consecutive lines with commented using sections result in ArgumentOutOfRangeException in SyntaxEditor with CSharpFoldingTagger.

Shift + Alt + Down Selection then typing multiple characters results in all of them being typed in all selected lines.

Shift + Alt _ Down Selection then typing multiple characters results in only the first one being typed in all lines, then selection is lost and next chars are inserted in the last selected line only.

When using LineHighlightTagger a NullReferenceException is thrown. To workaround this exception, you can add a custom TextFormatDefinition object to the TextFormatDefinitions collection of the RadSyntaxEditor.

this.syntaxEditor.TextFormatDefinitions.AddLast(LineHighlightTagger.LineHighlightFormatDefinition, new TextFormatDefinition(new Telerik.Windows.Controls.SyntaxEditor.UI.Pen(new SolidColorBrush(Colors.Gray), new Thickness(1))));

Single line folding regions is falsely recognized (by default it should be avoided) and messes up with outer regions.
For example
1 [

2 [ inner region]

3]

There should be no folding button on the inner line.  Collapsing line 1 does not collapse 3 but only 1 and 2 which is wrong.