Perhaps the Cas board asked Wigan if they would let any players go to the Jungle. Wigan agreed and Ainscough arrived and played!
Perhaps the Cas board again asked Wigan the same question and Tuson arrived.
No doubt someone at Wigan asked if any Cas player was off contract and Cas wouldn't be able to afford to retain him and Shenton's name popped up!
He's OOC end of 2010 and he'll want to secure his future with a decent salary.
Shenton is a quality player who'll want quality money. Wigan will have shed loads available after 2010 after releasing players and one or two retiring.
Wouldn't surprise me if he ended up at Wigan with one or two players going the other way.