Errors are human nature. Say 1 in 1000 times you mishear, misunderstand, forget the clearance, but the guy in the other seat rectifies your error. This will be the 1 in 1000000 where both pilots missed the call (or lack of it) simultaneously. I would not be surprised distraction from Spanish ATC was a factor. On many occasions in Spain I have had ATC transmitting in barely intelligible broken English a multitude of non-timely information such as turnoffs, taxi routings, parking stands, while we're flying down the approach trying to configure the aircraft and complete checklists. As for monitoring 121.5 whilst on approach and inviting more distraction and noise - no way.