Two stories.
One, I was leveling a new character with two friends... very late at night. I wanna say 3-5am or so. And I'm new back to the game around i23 or i22, after having left around the second month after Going Rogue for personal reasons.
We decide, hey, lets sewer sweep! It'd been forever since anyone we knew had done it, and DFB made it pretty irrelevant but it was a flashback. We'd all leveled a toon or two that way, so it seemed fun! So we're down there... and all of a sudden... A RIKTI?! I freak out, try to target it, run away, I forget now, then it goes away, we keep fighting. A bit later, an IDF trooper?! This happened many times before I found out there were now costume powers to allow you to achieve such tasks.
But they kept it up, messing with my head for nearly 15 minutes.
Then one time I was exploring on my redside toon and this happened.
I cannot tell you how, or why, only that I did not alter this screenshot in any way or cause it to happen by luring enemies to this location.
edit:
Yeah, I remember civilians in Founders Falls that thought there was a bridge where no bridge existed, so they climbed into the air and walked 12 feet off the ground.
As for the guys in Portal Corp, I'm pretty sure they walked through walls right to the end of the game.
Didn't the Portal technicians have some buddies in the tech contact office under City Hall?
This reminds me of all of those missions where you would save someone... and they would RUN full speed back into the mission proper from the entrance. That happened right up to the end.