[1.05 Invisible ceiling]

I've noticed something similar.

Alien on outside roof of ground floor. Troop in street throws grenade up killing alien & destroying the roof of ground floor/floor of 1st floor.

The destroyed area blocks and the invisible/destroyed area can be walked upon.

I expected my troop to fall down & break a leg but nope, his anti-grav boots kicked in.

[2 years of waiting and I finally installed!]

For me it's been years of searching for an X-Com (original) re-working & I stumbled across this on humblebundle. Just completed three ground missions & am so please how close to the original it is. So glad I found it now and didn't wait 2 years like the original poster, don't think I could have held out that long anyway.