I agree, he's always looked dodgey when a ball comes in - I remember earlier this season he dropped a simple ball - had to make 3 saves within the space of 5 seconds because he dropped the ball in front of a striker.
His catching is suspect at the best of times and Southamptons 4th came from a mix-up between him and a defender (sat in Telegraph stand, couldn't see who).
Dunn's looked far more assured in the 2 games he's appeared and both times has made cracking saves in the process, catching off his line impressed (first attack from Derby 2nd half, a deadly ball in from Derby's right wing - in wet conditions and caught without hassle).
I don't mind keeper's making mistakes - they get noticed more because it can directly lead to goals, but surely Murphy has had more than 1 chance and, if he know's he'll never get dropped, then he's not gonna improve.