I find it neat that those of us a bit OCD about symmetrical ship designs sometimes no longer have to obsess about placing ship components on the port/starboard centerline if we can only spare an odd number of that particular component and want to maintain symmetry with the ship design -- in other words, if we only have enough available mass for components for one engine, the attachment points on the ship sometimes automatically visually mirror that component if we place it on, say, a port connection point away from the centerline.  Its purely cosmetic, of course -- it doesn't actually double the component in terms of consumed mass capacity nor how much thrust the mirrored engine provides.  I think its a neat feature, but unfortunately its highly inconsistent -- its very hit or miss from hull design to hull design whether equipment installed at some attachment points mirrors or not.  In the grand scheme of bugs and issues, its a very minor one, a polish to fix up before release, but thought I'd mention it.