There is a common misconception (perhaps held by the majority of players and coaches in England, Didds of course excepted) that a "clean catch" is needed before the backs can be held back 10m. In fact, no catch is needed at all. The lineout starts when the ball leaves the thrower's ahdns; it ends when the ball or a player carrying it leaves the lineout; or when a maul or ruck that forms around the ball has fully moved beyond the line of touch.
So if the front pod moves forward, the back pod moves backwards and the poor throw lands in the middle, then if the ball doesn't leave the lineout the backs have to stay back until the rear foot of the ensuing ruck or maul moves beyond the line of touch. The same is true if the ball bobbles around from finger tip to finger tip before being caught, or if it is dropped (not backwards) by a would-be catcher.