place a unit carrying chemlights in the editor and throw one on the floor, in a building. It should clip through it.

While it is a minor visual glitch in the game, it is really an issue for modding and scripting. For instance I had a flashbang script working with a previous version (before 0.54 I think) and now it doesn't work because I need to check the line of sight between an object (representing the flashbang) and the player. In buildings, the LOS is always obstructed by the floor because of this bug...
I managed to fix this in my script, but I am struggling again with that issue for an addon.