In a Text Display Object using the Rich Text option you can only have the Line Breaks set to Word Wrap or Don’t Wrap. Any other setting will ignore the rich text tokens and display things as plain text. The rich text tokens will not be displayed like they would if you turned rich text off but only ignored.
The only possible solution to this would be to disable or remove those items from the pop-up menu when the Rich Text option is enabled. Or – could disable the Rich Text checkbox if anything other than Word Wrap or Don’t Wrap is selected. Ether way, Apple’s NSAttributedString class (which is used for rich text) doesn’t support these alternate line break options.
A mention of this restriction in the documentation might be be enough to avoid confusion. I noticed in the Text Display Object page of the Help file that the Line Break and Rich Text options are listed one after the other and would probably be a good place to insert the warning.