[Mobhack]

Its always been that way, since SSI allowed entry into the same hex as an enemy back in SP1 days - probably one of the later patches to it. Previous to that, you could not enter a hex with an enemy unit in it (though sometimes you could, if you moved multiple hexes and that took you into one that had been hidden. But if the enemy was located, there was no way into that hex until the enemy was a wreck.)

Slot 4 has always been weird - its meant to be for hull-mounted weapons. My guess is that the code that does bearings allocation for a fixed weapon aborts at range 0, since range 0 never occurred in the original game.

I have also noticed that if I try to fire one weapon at an enemy in the same hex, then all weapons will fire - but usually not the slot 4 one.

Now on our to-do list to fix, if it is fixable.