When I mirror elements across a regular line (draw group) they have a symmetric relation automatically. Why is it when I do this with a centerline (annotation group) there is no automatic symmetry applied? You would think it would. Thanks.
Because the centerline is, as you point out, an "annotation", and as such only gets momentary positioning reference, whereas if you use a sketch line, that physical geometry is then able to persistantly drive the mirror axis, giving the user automatic symmetry by the system.