this will probably not fix the automatic unrar and the automatic repair, however:
IF you really need to do a repair on one of these fucked sets (if an actual file is incomplete), then just load one of the actual par2 data files (not the small one) and start quickpar with this file (instead of the small one) - the actual data files contain the correct set of files to repair (and do not include the par2 files themselves) and you should then be able to do a par2 repair.
...and of course this is not an abz bug, but a problem with the software that created the par2 files.