I ran into a MAV this morning. I was messing around during the intro sequence, then paused the game to eat breakfast. upon returning around 10 minutes later, the still paused game had encountered a MAV.
Steps taken:
Start a new game in vanilla 1.0.4 with intro sequence enabled on Euclid Difficulty. Follow the intro guards to the catwalk just before 173's containment chamber, then enter the console and enable godmode and noclip. noclip around until the guard loses his patience and says he will just get another class D. pause the game. leave the game idle for up to 10 minutes. During this time a MAV should be encountered.
Specs:
Windows 8 64 bit, 16 gb 1600 mhz ram, gtx 770m, i7 4700 MQ
Spoiler
I'll look into this myself (or at least see if I can reproduce it with the Blitz debugger enabled) when I have a little more time.