Factorio Forums

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

In before *not a bug*.

This is intentional to stop fluid mixing IIRC.

As said: that's intended. It also prevents fluids from flowing where they aren't meant to before robots have a chance to finish building everything. The same applies for underground belts.