Ok, I`ve played FO3 about twice on my third run through- never saw this before:

Was in Rivet City talking to that Dr. Lily Allen or whatever her name is, about where my father was. Afterwards i decide to leave, but saw a different door I hadn`t tried. So I decided to walk in to the room. Well I was in for a shock, since two ENORMOUS Radroaches were in the room which looked like some kind of generator room. They were massive, like the virtual size of a double decker bus! I weaved around them and they seemed peacful at first, but then they started that agitated flapping crap and I just decided to shoot as I didn`t want to wait and see what being bitten would do to me. Me and my AI companion wasted them.

But what was that about? No one in Rivet city mentioned about giant bugs stuck in a room- There was no warning, no nothing. I thought it was a bug, but they are even called `Giant radroaches`.

I wouldn`t normally ask, prefering to find out myself, but no one in Rivet city seems to even acknowledge their existence!

Which mods are you playing with?

Running Attentater's Wasteland Economy, I presume. Dr. Li has no knowledge of what lies behind that door, nor does anyone else.

I was running that Mod. So that`s what did it?

Hmmm. I have so many mods that it`s hard to tell what`s Mod and what`s vanilla. Can`t see the point of it. It was silly. Maybe I`ll remove that Mod then.

Thanks anyway.