All,
A little hard to explain, I have uploaded a YouTube Video here:
https://youtu.be/dqpP0qK9KqU
Basically the problem is when you place an underground belt on a ghost blueprint the secondary part of the underground belt does not rotate correctly.
If you place an underground belt outside of a blueprint ghost, upon placing the first segment of the underground belt the second segment rotates automatically to match.
This does not happen when manually placing over a blueprint ghost.