Maybe it’s accidentally eating the comments? I can’t remember.
Also, hey, look at that – september has almost rolled through and it’s still very, very broken.
Maybe Benzilla can help you? In any case, the basic ideas are pretty obvious in bbsync; just create meta-entries for each sync’d item on both sides, so you can use them in functions to make links and the like. Comments -> posts just uses a standard comments hook and the bb api to create a post. If I were trying to fix this I’d probably go back to basics and work it again from there, using the old (bad) code as a reference only; that could be the approach to take with this.