This is a well known problem with filling your inventory too full and the cleanup script.
The cleanup script is necessary to remove corpses, unlooted drops and random junk thrown on the ground.
When you drop an item you must follow these steps or you may lose the item at the next area transition:
1) Pick up the item
2) save (remembering orb, rest, or /o c save)
3) Relog before going through any area transitions