I discovered that styling empty table cells works while editing, but the formatting is lost when the RadDocument is converted to RTF format and back again.
I have created Test() method to demonstrate a simple conversion that does not work.
var provider = new RtfFormatProvider();
var rtfString = provider.Export(_radRichTextBox.Document);
_radRichTextBox.Document = provider.Import(rtfString);
Attached is a 3 step process outlining how this is breaking for me. Thanks for the help.