[Mass Effect 1] "UNC: Listening Post Theta" not triggering

The three quests "UNC: Listening Post Alpha", "UNC: Listening Post Theta", and "UNC: Depot Sigma-23" are all somewhat interconnected in the original game.

Unfortunately, I haven't been able to get the "UNC: Listening Post Theta" quest to trigger properly.

Entering Erebus, you get a message from Hackett that triggers the "Listening Post Alpha" quest, but even if you finish this one you don't get any kind of notification or call about the other quest or its location.

You can still go to Acheron, enter the base, and kill all the enemies -- but only after all that is done you'll get a log entry for finishing "Listening Post Theta", and a description hinting at the connected "Depot Sigma-23".

Bug?