Just had situation where a unit staring down a corridor was shot by my and kills him from the direction he's facing but he didn't see the unit just heard him. Yet the unit must have been able to see him.
I'll have a look and see if I can recreate it, although to be honest it's probably a case of slightly different pixels being checked depending on the direction, and the corner of the wall was only "caught" in one direction. Is it the bottom-right of Moonbase Assault?