[merlight]

That's probably by design. The items are not actually moved immediately, your commands are carried out after your handler exits.

Some time ago I wrote my own function for finding an empty slot, which allows me to start the search after the previous one:

local function findEmptySlotInBag(bagId, prevIndex, lastIndex)
    local slotIndex = prevIndex or -1
    while slotIndex < lastIndex do
        slotIndex = slotIndex + 1
        if GetItemType(bagId, slotIndex) == ITEMTYPE_NONE then
            return slotIndex
        end
    end
    return nil
end
 
-- usage
local numSlots = GetBagSize(BAG_BANK)
local emptyIndex = findEmptySlotInBag(BAG_BANK, nil, numSlots - 1)
while emptyIndex do
   -- we have an empty slot in bank
   ... put something in there
    emptyIndex = findEmptySlotInBag(BAG_BANK, emptyIndex, numSlots - 1)
end
-- bank full