[MC1.5.1][1.52] Items dropping from wrong slots

I have a simple for loop to select and drop items from certain slots. If there is no item in that slot, it is dropping from other slots.

for i=4,16 do
  turtle.select(i)
  turtle.drop()
end

If there are items in slots 1-7, it drops items 4-7 then selects slot 8 and drops slot 1.