I used a sword to pop or break a double chest to pick up items (thought it was easier to do then to manually grab and move each item - "guess I was wrong"), it seemed like after my inventory filled up and items scattered across the floor, it allowed some items to flow into the wall behind where the chest was and wouldn't let me get them back or they start to disapear after a certain amount of time (10 -15 minutes).

I even came across this at an old site where I died when I got lost, while trying to pick up the items and clear out my inventory to make room (I wanted to get the rare and hard to craft items) they started to disappear before I could get them all. I was happy to find them as I thought I lost them completely but that quickly changed to disappointment again.