Explodes. Seriously.

I've sided with Yes-Man, but because my reputation with the NCR was still good I got the optional objective from Yes-Man to prevent Kimball's assassination, before using some chip somewhere. I go to Hoover Dam, and then one of two things happens depending on what I do.


1. I kill the sniper, disarm the bomb, but don't tell Ranger Grant anything. This results in the president finishing his speech, then he goes up to the vertibird and then just stands next to it, forever. Nothing happens, I can't talk to anyone. I've tried pushing the president around, but nothing happens. This is when the engineer for some reason doesn't attack.

2. The same, but I do tell Ranger Grant about one of the attempts. Or the engineer does attack after the speech and I kill him. Either way, the president panics and runs into the visitors center. There, on the upper floor, is a small room that was previously locked with 'very hard'. It's now unlocked, he and his 2 rangers go inside, stand in the corner by the cupboard, and a random explosion kills them.

I've checked, there's nothing in that room, or on the ceiling below it. It seems unavoidable. Does the game simply not let you save Kimball if you've sided with Yes-Man, and just makes the president run into that room (if he's not stuck at the vertibird), where a random unavoidable explosion happens?