I'm fairly certain the flag worked a while back, and gun traps and flame turrets were not triggered by players when the flag was on.
PvE players mostly just use Autoturrets for the NPC's and bots and that works as intended.

TurretsIgnorePlayers should not work for gun traps and flame turrets

TrapsIgnorePlayers includes gun traps and flame turrets

it worked because it was bugged and no one reported it for ages :D