What's odd about the Lucas thing is that as mentioned by GrkStav, Lucas checks his shoulder more than pretty much anyone.
Look out for it next time we play - he has rather an emphatic movement of the head before asking for the ball. It's in stark contrast to someone like Henderson, who is content to play back into defence and take the easy option, when turning out to face the play would be preferable.
Lucas as a sub is not quite as effective as Lucas the starter - he's not as good as Didi Hamann was, for example, at joining a game and making the tempo suit him. It's still a rare mistake for him to make, as his awareness is one of his major strong points, but a mistake it was, and a notable one due to the lack of pressure on him when he initially looked to receive the ball.
Hopefully, it's a fluke. He's not been anywhere near his best since his injury 18 months ago, but he's still a decent player and a very useful option to have. He came in to the game late, had a brain fart, lost the ball, and it led to us giving up a goal. The good thing about Lucas is that he's an intelligent player... I don't imagine it happening again any time soon.