Piloting and "Un-piloting" a camera Actor in viewport pane causes other viewport panes to reset its view orientation upon "Un-piloting" of Camera Actor.
Project has been attached for easier replication/reproduction.
Result: The second pane viewport camera resets it orientation after unpiloting camera actor in pane 1.
Expected: The second pane viewport camera stays within its original orientation.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-68146 in the post.