RtfFormatProvider of RadRichTextBox does not recognize zeros at the end of the tags. This leads to incorrect render of tags. For example: tag - \highlight0 is render as highlight with font color instead with transparent highlight color. tag - \b0 is render as a bold text. tag - \i0 is render as italic text. and etc.
RtfFormatProvider of RadRichTextBox also does not recognize \b0, \i0 (bold, itallic) endings. From the point it loads \b or \i, the rest of the text to the end gets bold/itallic. This should be able to be reproduced using originally provided rtf sample.