Missile Defence module visuals were reworked in some update, but I still believe this is a bug.
From what i know, if you destroy a missile, it will still keep a lock on you fly towards you and will not be terminated, but you will receive 0 damage.
However, there lies a problem.
Special Ops - Defiler usually fires the missiles with the green glow effect and even if Missile Defence module is used (Guard frigate), you still don’t know, if it is disarmed or not.
You still have a lock, it still tracks you and even if missile defence was used against it, it hits you, but you will receive 0 damage.
I am unsure, if this is a bug, but here is the screenshot:
Screenshot info: Missile defence was already used against the “green projectile”.
Upon impact I received 0 damage, I think.
Solution, if not a bug:
Either terminate the entire missile or change its glow (75% less glow effect), so that a person will know, that this missile or projectile was disarmed. Disarmed torpedoes should also no longer track you!
I think it is a bug, because the missile still tracks you and will always hit you, but you will receive 0 damage! This is an old bug, but I know that missile defence got slightly tweaked (visuals).