In my old game, I would occasionally find the companions that are supposed to be hanging out at Lucky 38 roaming around Vegas. I once caught Lily walking along the Strip towards the 38 in the middle of the night. Another time I caught Rex picking a fight with thugs in Freeside. I had seen both of them in the lucky 38 between me using them and this time.

This leads me to two theories.
1) Companions get bored and will go on strolls if you leave them alone.
2) Companions who slow travel back to 38 will end up back at the location before they're done travelling, effectively placing them in two locations at the same time.

A third theory is that I have dissassociative identity disorder and my other personalities like to take companions to random locations and make them walk back.


Edit: A fourth theory is that since I like to dismiss companions while in the 38, they go to an arbitrary location outside of 38 before turning around to go to the 38.

thats a mental disorder akin to schizophrenia... maybe you should put away your 'stealth boy' for a while