Thank you for explaining this :)

This has happened to me too, it's really frustrating, isn't it! I think it's because you run into the corpse (just like running into another player moves them a little)

I have experienced this several times (unfortunately for you, I am on the bandit wagon!). I think it's combat loggers..

Yeah, If you have it in your hand and press tab you can still add items to it, but it will not show you the empty spaces. It works fine if it is on the floor though