I have no doubt that Hacking was a problem missionary, but I think it is unlikely that he was sent home for having a sexaual relationship. If that was the reason, it would NOT have been an honourable release and he would have faced a church court when he got home to determine if he should be disfellowshiped from the church or not. Nor does the church keep a rap sheet of a member's past sins, so there is no 'report' to come out.
When a missionary is sent home for disobedience, it usually sparks a lot of gossip and speculation. He could have been sent home for not staying together with his companion elder, but that doesn't make an exciting story. Unless there is an eyewitness coming forward on this matter, this should be counted as nothing but gossip.
Thanks, Grig, that's helpful for those of us who aren't that familiar with this religion.