Maybe there's a halfwave plate on the output end of the optical train on each of the lasers? If this was the case it wouldn't matter what orientation the diodes were as the halfwave plate would rotate the polarisation on output to whatever orientation the plates were set to.
Jem
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