In the early days of arcade-adventures (or RPGs as they later came to be called) you’d often collect some prized weapon or treasure, and find the “room” you were in suddenly filled with some manner of enemies. Since this was also the age of ‘insta-kill’ tricks where you were allowed to be killed with no warning just for stepping on the wrong tile (which you’d know to avoid next time) then this was accepted.
Nowadays that’s often seen as a bit unfair and so while enemies may spawn as a result of you gaining some item, it’s often done “off camera”, so that when you make your way out of the dungeon/maze/building, you’ll encounter the new enemies rather than immediately.
Old World Blues (OWB) seems to have missed the memo on this, which is a little strange given the rest of Fallout: New Vegas (FNV) has been very good about it.
Three times now, enemies have spawned in such a way that it was obvious that they weren’t there before, but were after I’d achieved some goal. In one case, three of the damned things spawned on top of me! We’re almost going back to those early insta-kill days.
Old World Blues does so many other things so right that this is surprising. And annoying.