title: wrong lua table size when using string key index
body: <p>Usually for getting table size, the standard table library function # operator works.</p>
  
  <p>However when I make a table which has a string key index, it doesn't work.</p>
  
  <pre><code>local function addWriterIdListToTable()
  
          local returnTable = {}
          local requestString = "1234:16 5678:8 9012:1"
          local idList = requestString:split(" ")
          for i,v in ipairs(idList) do
                  local oneId = v:split(":")
                  returnTable[oneId[1]] = oneId[2]
          end
  
          for k,v in pairs(returnTable) do
                  print (k .. " " .. v)
          end
          print("size of table: " .. #returnTable)
  
          return returnTable
  
  end
  </code></pre>
  
  <p>I want to trsnform a string to table.
  The function "split" parse a string, split it with parameter as a delimiter, and return as table.</p>
  
  <p>The result of a excution above function like below.</p>
  
  <pre><code>1234 16
  9012 1
  5678 8
  size of table: 0
  </code></pre>
  
  <p>It shows the content of table exactly as I expected, but its count is not.</p>
  
  <p>Anybody to help me?</p>
  
  <p>Thanks in advance.</p>