Usualy you can only place defenses near the dummies in the public tavern. In all areas it is not possible to do so. The EV2 can workaround it, by starting a build, then pressing "e" it is possible to place the defense down. With that EV2 can place anywhere in the town her defenses. Repro Chance: 100% Steps for Bug Repro:
start the game
in the public tavern choose the EV2
press a button for placing a defense, outside from the building area
notice you can place the defense.
Expected Results: EV2 can't build outside of the building area.