I want to bring this issue up again, since it can be reproduce and get some fresh eyes on this issue,which has been around since 4.0 and still hasn’t been resolved in 4.5.1.
There is old answerhub thread: Normal Map Workflow with Xnormal is not working - Programming & Scripting - Unreal Engine Forums
However more useful info about this bug can be found here: http://www.polycount.com/forum/showthread.php?t=141659