I would have to vote for a glitch in Fallout 3, as well.
*Spoiler Alert*
At the finale of the original, right before Broken Steel starts, when you have to start the purifier in the memorial.
I had just led the assault and cleared a way to the rotunda door. When I stepped through, I was immediately confronted by Col. Autumn. We had out witty banter, and I let him live. He ducks through the other door, I smile to myself, and wait for Lyons to start her bit about what we have to do next.
Only, it never begins.
I turn and realize, she's nowhere to be found. She didn't come into the room with me. the door is locked behind me, barring access to where she might be. The door that Col. Autumn exited out is locked as well, making sure I find to egress out that way. And, of course, the door to the purifier is locked, keeping me from making an ultimate sacrifice so that I can end the sequence.
basically, I'm locked in a room with no way out. Not even console commands can help me in my personal hell. I go to reload my previous save, to find that it has been somehow corrupted. Lyons is nowhere to be found. I literally had to restart from a save made hours previous.
Now, I with my overactive imagination, pictured the events somewhat as thus...
*Lyons is standing out front of the freshly liberated purifier with what remains of Lyons Pride*
Lyons: Well, it's been ten minutes since he went in. No sign of him yet, but all sounds of fighting have stopped. Col. Autumns vertibird took off five minutes ago, even.
Pride member: Maybe he needs help?
Lyons: Nonsense! He single-handedly took down President Eden and disarmed the nuke at Megaton. He's practically a demigod. A true Wasteland Savior. Who are we to try and help one like that?
Member: Well, why isn't he back yet?
Lyons: He must be working the purifier already! *stares wide eyed at the nearby water*
Member: Wait? What? There's no sign that anything has happened yet.
Lyons: Are you a scientist? Do you know what to look for? *rushes to the water's edge, lay facedown, and begins taking greedy gulps*
Member: Ma'am! That could be dangerous! That water could still be highly irradiated!
Lyons: *looks up, hair starting to fall out and smiles. A tooth falls from her grin* The tingling means it's working!
*Lyon's dies*
Member: Oh, for god's sakes. *takes holotags from her corpse and kicks her body into the water* We'll tell Elder Lyon's she was killed in battle. Let's go, Lyon's Pride.
*they all turn and begin marching back to the Citadell, leaving me forever entombed in the purifier room, inches away from the button that would remake the Wasteland into a new garden of Eden.*