Half Life 2 bug

I was playing HL2 on my Xbox and something funny happened...I found that while going from one area to the next, if I was in the exact right spot when it started loading the next area (found the spot by random chance), it would spawn an Alex right in front of me. She would walk, say "excuse me" if I bumped her, etc...though she would not fire her gun, open any doors and the other NPCs entirely ignored her. It was funny when I got to a spot where the real Alex was SUPPOSED to be...