When attaching a parachute to an object to then drop it from the sky, once that object reaches ground level the attached object actually sinks below the terrain whilst the parachute collapses, detaches and deletes. once the object is detached it will fall through the terrain (small objects) and is not accessible. larger objects (eg vehicles) tend to glitch the terrain and get thrown high in to the sky which results in damage to the object.
Screen shots below to show the effect.
crate goes below terrain whilst attached to the parachute.
parachute folds over, detaches from crate and deletes.
crate then falls through the terrain.