Well I think I actually found a flaw in the software...… advice from SQL Server forum was to be sure the field property in the table was nvarchar(max) - which it was
So the only work around that I can come up with is this:
1. make the text box control unbound
2. set the text property to Rich Text
3. set the text box's control source back to the table/field
If you do it this way - the Rich Text property sticks and the control works correctly as Rich Text.....but if it is bound to begin with, as noted, one cannot change it to Rich Text for some reason......