If a ghost pipe to ground is placed between two existing, connected, pipe to grounds, the flow between them is stopped.

Pictures: https://imgur.com/a/SXSPydQ

Yup, just came back to update that the first click doesn't matter. However it seems to quick-replace if you drag over them quickly.

What did I do?
Clicked and held on an existing belt, got the "Transport belt is in the way" message, dragged over an underground belt expecting it to be replaced with belt, but nothing happened.

What happened?
Underground was not quick replaced. Belt was placed on empty tiles. Underground was ...

When the production window is opened, you can normally select individual items to see only selected items on the graph. When scrolled all the way to the bottom, items aren't able to be selected until I scroll all the way back to the top. Same things happens on the production and consumption sides.