I am currently working with a forum recently imported from SMF 2.0. Import worked correctly; however, many messages which were displayed correctly in the SMF version fail badly in XF, to the point of being unreadable. The BBcode was not corrupted during the import, as verified by a check of the database directly. It seems that there is a major fault in the BBcode renderer in XF, one which also replicates on xenforo.com (here). There are many more examples, which I can provide as I slog through them.