I'm FREDding a (standardish) convoy escort mission and I ran into a problem.
You have to escort three Elysiums from Point A to Point B. The first two enemy wings (Leo and Pisces) arrive simultaneously and attack the convoy. All the directives are there. So far so good.
The second wave of enemies (Cancer and Taurus) come in a minute or so after the first wave, but the "Destroy Taurus" directive doesn't appear until much later. This is what the directive window looks like on the second wave's arrival:
Defend Witch Hunter
Defend Defectors [2]
Destroy Leo
Destroy Pisces
Destroy Cancer [3]
I'm assuming that the pending "Destroy Taurus [4]" directive should override one of the already completed ones, right? It never does. You don't see this directive until they are dead or killed your transports.
There's nothing extraordinary about any of the enemy wings or the directive events themselves.