To clarify by "spotted", I mean a physical graphical representation of an assault gun is displayed when said assault gun starts moving even though the nearest unit is over 60 meters away. As I understand the rules of the game, a graphical representation of a unit should only appear when the unit can be seen by an enemy unit. I tried duplicating this effect with just plain fog, etc and did not see this behavior - in those cases a sound contact marker would remain in play until the AFV actually entered LOS at which point the graphical representation would appear - as expected.
This bug allows me to, among other things, know the exact facing/orientation of an enemy AFV even though it is not within LOS of any of my units.