Map package variable breaks the contract execution without exception

[piux2]

package maptest

var m = make(map[string]string)

func Deposit() string{
  m["0xABC"] = "10ugnot"
  return "Deposited"
}

The maptest contract does not return anything when Deposit() is called a second time. The contract seems to have stopped executing before the return but no panic or exception.