There have been several occasions where I have fallen through solid blocks to my death. I am not digging directly beneath myself, but a block or two to the side. It's happened in the nether and over worlds alike and each time my inventory has despawned in less than 5 minutes. For the most recent incident I was 3 blocks away from gravel, with none above me, and got burried in stone. By the time I found my way back all of my supplies despawned. I got close enough to see my arrows and misc. blocks from mining, but was unable to collect any because as soon as I reached where they were they were gone. It was less than 5 minutes from death to finding the location. I have also died, respawned on top of my house instead of my bed, and died instantaneously.