Heya,
Lovely mod, it's useful when using a bus!
I was playing around with it and when I was using red underground belts, the offset was wrong:
When dragging (normal) red belt from right to left there appear 2 belts above the cursor position, whereas dragging underground red belt from right to left the 2 belts appear below the cursor position.
Nothing too big, and easily to work around when you know of it. It is just not expected behaviour.
Thanks!