IIRC, I think I solved this by using List instead of Collection.
AFAIK List extends Collection, so it doesn't matter what interface to use, and actualy I used List and Set, thought named them as Collection.
Maybe this link will help:
I don't have my code handy where I'm at, but I know I changed many of my collections to another type to work around this.
Thanks a lot, I've replaced List with Set and now it works!