I just noticed the same problem (or "problem") with another unit, a vehicle-jeeps carrying SS-11. This one has 1 ammo left and 2 damage.
1976, Greece, I think the slot number is 058.
Now, since this is a vehicle, it could be different than with the inf, but I thought I would post it anyway. It could see 2 enemy vehicles (one is now destroyed by an AMX-30) and still not fire at them. In fact at first it would show the number 1 at the bottom of the page where the fire shots appear, but as soon as I pressed T and F, it refused to fire, nothing happened on screen and the number from 1 went to 0.
Oh, I forgot to say that this one is from a single player generated campaign.