If Berta firing at will, or right-clicked to attack unit\structure it will fire somewhere outside a map, and only when you oders to fire thrue attack button it shoots correctly, this issue discovered on default map SmallDivide
The unit it tries to attack is probably to close to it to be in its range, in this situation the bertha will raise its turret and shoot outside of its own range.
Solution - dont build them on such tiny maps (why would you need one?)