Hope this helps!
page 10, Twilight Imperium FAQ and Errata v 2.2.1 - Updated 3/20/2009 wrote:
Q: If I take over an opponent’s Space Dock with a Shock Troop, can I build at the Space Dock this round?
A: No. Whenever you place a new Space Dock piece on the board, it is treated as if it were built this game round.