Some weird visibility bug?

[Alpha Centauri Bear]

Save attached. Press Alt and see detected alien location in front of the tank. Try to move it right at this location. It won't be able to since alien is staying there but it won't see it being adjacent to it. Only after few turns around itself the alien is revealed.
I also noticed the same when I uncovering map. Some dark tiles are not getting uncovered even when I am adjacent to them and am looking right at them. Only after turning around the axis they somehow get revealed.
I noticed this with tanks but not soldiers.

I am playing forked BAI but for now it should be identical. I just updated it to be the same and compiled.

[Alpha Centauri Bear]

Mystery solved. Apparently, when alternate movement methods is on, tank sees with its turret. So turning turret toward the enemy allows to see it.
When this is off tank sees with its face even if turret looks some other direction.