I am pretty sure this in not an intended effect of Lockdown, but it seems to be permanently granting Earthbound, not just within the area of effect. I deployed an Angel of Restoration and on my next turn deployed a Privateer Captain. The Angel of Restoration lost Flight for the rest of the game (she most certainly moved away from the Privateer Captian, but to no avail).
I tested rather extensively: http://forums.poxnora.com/index.php?threads/bug-compilation-thread.467/page-11#post-28956
Good to know. The time it happened to me (above) the Angel of Restoration was the one to leave the area of effect and lost Flying. It fits your observations.
