If not what HW3 mentioned it's just Lorient being evil again,.... it's the toughest port for the AI to deal with for some reason, sometimes everything goes smoothly, your escort does what it's supposed to do and they all live happily ever after once you've left the scene...
and sometimes you get shipcapades...
Believe me, it's been looked at and looked at, and then rehashed, and looked at and fixed, and fixed again...
It's just one of those things...