Chasing missiles fire slower if they are locked on to a target as opposed to being fire without a lock. I'm not sure if that's intentional or not but it seemed like a bug to me so I thought I should report it.
http://www.youtube.com/watch?v=rN2ljz_RNkA&feature=player_embedded
http://www.youtube.com/watch?v=rN2ljz_RNkA&feature=player_embedded