Moving of an mirrored object does not give the desired outcome I have this mirrored object (those green beams in the image below). When I move the object to the right I expect the mirrored part to go to the left but it moves also to the right. Why is this ?
In object mode, blender considers objects with mirror modifier a whole/complete object, just like a normal object. Therefore when you move it, you're moving the whole thing. However when you switch into edit mode, your mirror modifier start working as you edit, using the origin of the object as mirroring center pivot. Beware that the modifier will take object rotation into account, meaning it does not uses global axis as its mirroring pivot.