"Hits so rarely" is perhaps a bad way of putting it: I can reproduce it consistently now. It hits very few people, for sure.
My latest tests indicate that unless you use journal_checksum or journal_async_commit (which implies journal_checksum), neither of which are the default, you appear to be safe. Unless you use nobarrier *too* (which you really shouldn't unless you have suitable hardware, which means battery-backed disk controllers: a PSU isn't good enough), you will see a journal abort and a readonly remount of the fs at next mount. You need both journal_async_commit *and* nobarrier to get no journal abort and silent fs corruption.
There may be additional conditions I haven't yet combed out: for all I know the latter case also requires the arcmsr driver or something. It's kind of hard for me to test that on account of if I configure that driver out, my machine has no accessible disks to corrupt filesystems on. :)