Common script does not work in the way I want

[Hadeel]

I have a function called "commpnPost()" in a common script as below.

I call this function everytime when there's a change in each KNX status object, so that I can let other servers know that there's a status change in the KNX project. 
I call it in each event script as the image below.   ('9/2/1' is the group address of the status object)
   

However, when I log the output inside the common script, I can see the first argument '9/2/1' somehow changed to '10/4/5'.
   
I also made sure that it already changed to '10/4/5' at the first line of the commonPost function.

This happens with other group addresses too.
Am I using common script in a wrong way ? Or maybe there is a chace that I need to clear inside LM ?

Code:

function commonPost(add, value)
  local dptString  = convertToDptString(add)
  local payload = ""
  if dptString == "dtDate" then
    payload = '{"groupAddress":  "' ..add..'","value": {"dtDate": { "year":' ..tostring(value["year"]).. ', "month": '..tostring(value["month"])..  ', "day": '..tostring(value["day"]).. '}}}'
  elseif dptString == "dtTime" then
    payload = '{"groupAddress":  "' ..add..'","value": {"dtTime": { "hour":' ..tostring(value["hour"]).. ', "minute": '..tostring(value["minute"])..  ', "second": '..tostring(value["second"]).. '}}}'
  else
    payload = '{"groupAddress":  "' ..add..'","value": {"'..dptString.. '": ' ..tostring(value).. '}}'
  end
  log('payload: ', payload)
  --**post the payload to a speficic REST endpoint  **
end

Code:

function convertToDptString(address)
  mapping = {}
  for key, value in pairs(dt) do
    mapping[ value ] = 'dt' .. string.upper(string.sub(key, 1, 1)) .. string.sub(key, 2)
  end
  obj = grp.find(address)
  dpt = obj.datatype
  if dpt then
  dtname = mapping[ dpt ]

  if not dtname and dpt >= 1000 then
    dtname = mapping[ math.floor(dpt / 1000) ]
  end
end
  return dtname
end