Austria (German) region is set in windows. Digit grouping symbol is set "," and decimal symbol is ".".

Inserting rounded rectangle shape in RichTextBox produces broken geometry like so:

In this case, the MergeField Code value without the brackets gets concatenated before the display name of the MergeField in the document. 

This reproduces after the document get exported and the DocxExportSettings' FieldResultMode property is set to FieldDisplayMode.DisplayName.

The MergeField is displayed correctly in RadRichTextBox. The issue occurs only when the document is displayed in MS Word.

To work this around, set the DocxExportSettings FieldResultMode value to null.

DocxFormatProvider docxFormatProvider = new DocxFormatProvider() 
{
	ExportSettings = new DocxExportSettings() 
	{
		FieldResultMode = null
	} 
};

The non-breaking space breaks the word if a comma character is presented in the word. For example, the following text should be treated as one word - 10,0 % but it is separated into to words - 10,0 and %.

The issue can be observed when the word should break on the next line. 

NullReferenceException when changing themes, the RichTextBox has TrackChanges enabled, and the current user is set.

Workaround: set empty user like this: 

private void RadRichTextBox_ProtectionStateChanged(object sender, EventArgs e)
{
    if (this.radRichTextBox.CurrentUser == null)
    {
        this.radRichTextBox.CurrentUser = new Telerik.Windows.Documents.Model.UserInfo(string.Empty, string.Empty, string.Empty, string.Empty);
    }
}