[v1.09 Ground Combat] - Sight and shooting through walls when at different elevation

On my way to attack a downed cruiser, there was a two-story building between the dropship and the UFO. This particular building has a hallway in its middle of its lower story leading to stairs, and then hallways in the upper story on either side going back and ending up in the same room.

While advancing outside the building I saw (through the window) that a wraith had teleported up to one of those upper hallways (the "northeast" one, if it matters). My plan was to keep the enemy occupied with a guy outside covered with smoke and moving my other guys into the hallway in the lower story, wanting to regenerate TUs before running up the stairs and starting to suppress it. The wraith somehow saw and shot two of my men through the wall down to the lower level. There was no visibility or line of fire to the enemy from the hallway below. When I had people get up the stairs, the wall worked as normal blocking sight and line of fire.

Apologies if this is already a known issue, and also apologies for not providing a savegame for illustration and debugging, I can imagine it's hard to fix it using only a text description of the problem. If I encounter the same thing again I'll try to provide a savegame.

In UFOs spanning more than one story, there is also occasionally a visibility bug causing a soldier to see the entire interior of another level, typically revealing the bridge or whatever you call the final room in the UFO, including enemy units in there. In these cases, unlike the building I wrote about, it is thankfully impossible to shoot through its walls/floor though.

I'm running 1.09 from GOG, no mods (holding off on those until I beat insane).

It's not a problem, thanks for the report. An updated line of sight system is one of the big improvements made in V1.5 so these problems should go away with the newest build.