You might try keyword searching the old forum posts (from the SourceForge venue). I belive they were all transfered here. My recollection is a thread with the issue of reference modes and subtyping was addressed before.
Check the libaray here, or search for Dr. Halpin's published articles on Subtyping - I'm sure I've seen a couple. They won't be tool specific, but should help with determining what's actually required by the theory.
As for the nORMa tool sample data editor, I think everyone would like that made more user friendly, and comprehensive, at some point. Sample data is important for validation, but if it's a pain to workwith, most tend to avoid the step. My guess is that general UI considerations are going to be lower priority than stablity and other issues. If this were a commercial product, the marketing folks would have that switched around.
Glad you found the probable bug. On the SourceForge site, they have (or did), a bug reporting tracker. Check to see if it's still active for the ORM project there.