While I was on the strategic screen (before the second fight), the "Militia" menu (the fist button) behave strangely: the button to assign automatically the militia through the sectors of the town created more militia each time it was clicked, and dispatched them to the truly friendly sectors of the town. I had groups of 26 militians ...

And another thing:
When the sector was in its strange state with non existant enemies, I tried to attack the militia. At some point, Vince was hiding on a roof and a message said "Vince hears a faint sound of movement coming from none of your merc have any medical ability", instead of "below".

I kept a savegame with 2 visible enemies and one with 1, one at the beginning of the day and one at the beginning of the hour before the attack.