It seems like a pretty good guess that the problem has to do with some file system that the document has gone through. Jesse, see if you can reproduce this with TextEdit, by writing out an RTFD document and moving it from one file system to another, and see if the resulting document will still open in TextEdit. If you have a reproducible case, definitely file a bug. (If you don't have a reproducible case, you might still file a bug, but it would be more difficult for us to act on it.)