Grimrock

I was creating my own dungeon and I made a room with one trapdoor and fireball spawners.
I managed to get one skeleton warrior to walk on to the trapdoor and the timer controlling the trapdoor opened it, so the skeleton started to fall down, but just before his head disappeared into the hole, fireball flew over the pit hitting the skeleton, so he warped back up, changed to his pain state animation and fell down again correctly.

Then there was another skeleton which did just like the first one, fell down, took a hit but he died. I went down from the same hole, and there was the spear and shield from the skeleton that died, but the other skeleton was there alive, and it seemed to be resistant to all damage. I tested fireburst and all the other party members used melee on it, but with no success.
I didn't get the "miss" message either, so it was like he wasn't there at all. He blocked my movement and he could hit us thou.

I only tested it once, but will test it again tomorrow and capture some video, I'll possibly make another dungeon replicating the room so I can upload it for people to see.
Anyone else had similar things happening?

never heard of anything like this, crazy!

I tried to mimic the room on another dungeon but it didn't work, gotta try playing my older dungeon if I could make it happen again!

Oh, I forgot to post if I could get this weird thing happen again... well, I didn't :I