Hi ,
I looked into this issue today, and it does appear that there is some unexpected behavior occurring here. I have entered a ticket explaining my observations to have this investigated further (UE-15025). There is one thing that I would like to point out, though. The LineTraceSingle function is set to be deprecated soon. It will be replaced with a new function, but I observed the same behavior in the new function (I mentioned that in the ticket I entered). I just wanted to give you a small warning that the source code here is going to change soon.