Infantry platoons using the Man Portable AA Weapon such as AA Mechanized Infantry, don't seem to recieve the -2 modifier for firing at airborn targets (specifically VTOLs) as listed in pg.274, aToW.
Granted, aToW is mostly a RPG thing, but the weapon does have the "A" weapon special effect, which may take place in the board game like inferno conventional infantry weapons, burst-fire infantry weapons, flechette infantry weapons, and so on.
This is as of .37.8
The original rules for this equipment is in Handbook:House Marik, pg 165.
Not sure if these rules have been replaced by something in TW/TM/TO.
One of the reasons I haven't done anything with this bug is that it's not clear to me how AToW rules are considered in TW...
Alright, so I got a clarification. The Rules in AToW are at AToW scale, not at TW scale. The TW-scale rules are in TM pg148 which clarifies what the "A" means, and that's just that the weapon allows infantry to hit aorborne aerospace rules. The HB:HM rules are supersceded by TW (TM). So, essentially MM is currently implementing the rules correctly.