If the Table's TableCellSpacing property is not divided by 2 when the document is exported to Docx or Rtf, this leads to incorrect rendering after the exported document is opened with another editor (RadRichTextBox, MS Word).

Workaround: Divide by two the Table's table cell spacing property value before export to Docx, RTF formats:
foreach (Table table in document.EnumerateChildrenOfType<Table>())
{
    table.TableCellSpacing /= 2;   
}