I used to know how to unlock it, but I can't be assed to remember right now. How do you unlock the camera after it focuses on an objective?
I'm pretty sure there's an "unlock camera" trigger somewhere. otherwise, open another map where you know it's used and see how it's made
It's in campaign. Like it will lock onto an objective, and just last week I was able to unlock it. I don't know if it's a bug or what, but I have tried almost every key.
The SC section is pretty neglected nowadays so if you don't get a response soon enough try sending a PM to Imagine. He knows all.
Focusing the camera tends to lock for an annoyingly long amount of time when you play in singleplayer. Play your map over battle.net and it should work.