This is not a bug. Scattergun turrets shoot vanilla shotgun ammo, and as such act in the same way, colliding with other entities in their path. There are simple defensive designs that work and not cause friendly fire. I'll add example image of such design in few hours (on mobile now). EDIT: added image of early game defences using scattergun turrets.
Same situation applies to cannon turrets if you use vanilla cannon shells. In this case however, simply use ammo provided by this mod to fix that.
