I had a bunch of high quality 532nm DPSS single longitudinal mode JDSU lasers with the same problem. The operation wasn't affected by the ghost beam at all.
As others have said, it's no big deal. Not sure of the cause though and would be interested to learn for future reference.
Quote: "There is a theory which states that if ever, for any reason, anyone discovers what exactly the Universe is for and why it is here it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another that states that this has already happened.”... Douglas Adams 1952 - 2001