This happens for example with music albums posted with a par2 set and also sometimes with some big files that were cutted with QuickPar (those files that QuickPar itself joins).
In those cases, Altbinz thinks that the par2 set is broken and it downloads all the par2 files it finds.
However, if I open it with QuickPar, the set is correct and needs no repairing.
I have a NZB that will reproduce this problem, if you need it.
Thanks!