I get quite often an Aft laser when buying a ship that should be able to have just Front laser. Happens both with native and OXP ships.
On one occasion the ship for sale had no weapon upgrades listed, and in shipyard.plistforward_weapon_type is set to EQ_WEAPON_BEAM_LASER - the ship had both Forward Pulse Laser and Aft Beam Laser fitted (yes, the weapon_facings is set to 1 in shipyard.plist).
In trunk the weapon facings flag is now used to figure out if the player can install new lasers in those specific facings (in other words, you could get a ship with 4 fixed weapon types & weapon_facings = 0). That would mean you cannot change any of the pre-installed weapons with others of your choice.
I'm not quite sure whether this bug actually classifies as a bug, or is just a quirk!
When a ship should be able to have only one laser, Forward laser, it is still assigned an Aft laser.
Further testing revealed this:
if in shipyard.plistforward_weapon_type is set to EQ_WEAPON_BEAM_LASER - the ship has both Forward Pulse Laser and Aft Beam Laser fitted
BUT
if I set aft_weapon_type instead in shipyard.plist to EQ_WEAPON_BEAM_LASER - the ship has only Forward Beam Laser fitted, no Aft laser
Looks like forward_weapon_type in shipyard.plist sets the actual Aft weapon and vice versa!
Alas, after further study it doesn't seem so straightforward...
Looks like there's something weird happening when a ship is bought and it is given extra equipment. The game seems to throw in random Aft weapons to all ships. Here "random" includes "none", and "all ships" means that any ship bought can get an Aft weapon regardless of equipment listed in ship purchase screen (no mention of Aft weapon upgraded to xxx) and regardless of weapon_facings.