Least Dragonmark of Finding is used on breakables to obtain temporary items. On vases and crates it usually works fine although occasionally the temporary item goes into the floor and can't be picked up.
However, when used on coffins (horizontal ones on the floor and the vertical ones standing up along the walls) the temporary item can't be retrieved. It appears to imbed in the floor right at the base of the now-broken coffin. I noticed that when coins drop they are shifted from the coffin to a spot accessible on the floor, perhaps the same logic needs to be applied to temporary items too.