Some items picked up are immediately placed into boot slot, mostly harvestable items e.g. watermelons, wheat, seed, carrots, potatoes. Some items are unthrowable
occasionally, such as iron swords. On placement of an item into boot slot, any previous items held there are destroyed and disappear. Only one type of item can be held
at a time, sometimes only one of each. It seems completely unpredictable which items will exhibit this issue.