In the rules for Oceans Eleven:
Groups of cards can be moved if there are enough Reserve piles free to allow the move if the cards were moved singly.
That means, as far as i understand, that you only had two reserve piles available when you tried to move the cards. In that case, it's not a bug, it's just part of the game rules.
I've tested it, and i came to these results. If you have three reserve piles free, you can move a stack of four cards, and if you have two reserve piles free, you can move a stack of three.