Solid Matter

I purchased the game a little while ago, but have just started getting into it. Last night I experienced something that may be related to the flying animals bug, but may be separate. After starting a new game I found a cave with a sloping entrance and canyon that I chose to be me temporary base of operations. A few game days after establishing this base a bear decided to camp out above it. The entrance was far enough away from it so that I could get in and out without getting attacked. At one point I was putting up stone walls inside the entrance to the cave and started taking damage. I moved and looked around and could only see a torch on the wall so I figured I burned myself. Shortly after this, I died without seeing a cause. After respawning in the canyon, I noticed the bear inside the cave (and behind my wall). A couple of deaths later I managed to kill the bear. This got me remembering other times where I saw a cow slowly fall into the ground. I am guessing that the bear had attacked me through the cave ceiling and then fell through it later. If the integrity of ceilings is not stable, I wonder about walls. Can you be attacked through a castle wall by an enemy with a sword outside? Either way, is this related to the flying animals or is this a separate bug? Ideas???