[1.60 Linux] Friendly Fire through 100% block wall

[Shoes]

Last mission, I managed to hit a teammate who was standing behind a brick wall. Here's how it happened:

In a farm level, there was a sebillian in the corner of a brick walled structure. Adjacent to the alien but on the other side of the wall was a xenonaut. With a second xenonaut, who was to the right of both these units and thus shooting in both their directions, I burst fired with a ballistic rifle. Of the three bullets, one hit the sebililan and another hit the xenonaut who was behind the wall.

I have a vague recollection of another mission there being an odd instance of friendly fire similar to this one. I don't recall hitting an alien from behind 100% cover, but I also don't try...