Steps to reproduce:
- Build a entity of any kind.
- Create a ghost entity any kind some where out of normal player reach from the entity in step one.
- Try to place a real underground belt on the previous entity in step one.
- Try doing the new underground belt-drag. omg you are placing those way out of normal placement range. O_O
Screenshot of it in action. Mouse cursor is over the fast inserter by my player character. The ghost is way off to the left of the screen and the to be place underground belt is a little way below that. Doing the belt drag works as if I was standing over there within range. Anything that would "break" the dragging procedure breaks this one too.
[edit] Just tested underground pipes too. They also do the exact same thing as underground belts.