seems like a bug, but you can finish the mission anyway (got the same problem only 2-3h ago
)
Just keep your mo-ship and the fighters which don't scout 4-5 fields right of the portal or maybe even further, you only need 1 ship with a 350 clicks sensor and maybe (!) some cheap cloaking device.
You can easily follow him and it doesn't matter if you come too close (you'll get some warning message) with a cloaking device. Kept myself at ~300 distance to him.
The only mystery seems that the mission is failed if you get a message from Ternie, otherwise keep on going. If successful, at the target station you'll send for reinforcements and the trigger for the governor seems to be a ship or mo-ship near the station where you got the mission (afaik, can't remember, there 'll be some text and that's it)
hth