I've noticed two things about flash since it was changed for the turrets. One, is that if you flash while you have turret agro you still keep turret agro EVEN if you flash outside of turret range. This means that the next turret shot that was prepping will always hit, even if the shot had not fired. I'm not sure if this is a bug or intentional.
The second thing i've noticed is that auto-attack or melee abilities WILL proc even after the champion flashes out of range. As long as you were within range of the target when he flashes your ability or auto will still hit him. This is definitely a bug.