I've run into an interesting bug which seems to have spared my last colonist. This entrance setup messes with enemy AI in such a way that they kept walking up and down where the selected tile is while getting shot by the turrets. The enemy wont even shoot the turrets most of the time. The only things to have shot them so far were pirates with incendiary launchers and they just killed themselves with them at that range.
http://images.akamai.steamusercontent.com/ugc/94973258561176468/CB0A28F58F924AF057EE6529EB55CE64EDA60BFE/
If I were to venture a guess as to why this is happening, I'd say it's because they get targeted by or engage a turret and decide to take cover from it by its nearby wall, but then get in line of sight of the other turret and switch to the other wall for cover.
http://images.akamai.steamusercontent.com/ugc/94973258561176468/CB0A28F58F924AF057EE6529EB55CE64EDA60BFE/
If I were to venture a guess as to why this is happening, I'd say it's because they get targeted by or engage a turret and decide to take cover from it by its nearby wall, but then get in line of sight of the other turret and switch to the other wall for cover.