You are wrong. I have used this method many times and it appends the entire field contents, no problem.
It's likely that your problem is caused by failure to refresh the back-end rich text item from the document you are editing. This is done by calling NotesUIDocument.Refresh(True).
Check your inputs. Display the Text property of the RTItem you're trying to append. Does it contain the text you expected?
If the above does not solve your problem, we need more information about what you're doing. If you're not sure what information to supply, the
C R I S P Y document might help you.
- Andre Guirard, IBM/Lotus Development
Useful blog: Best Practice Makes Perfect