Interesting. Not how I expected it to work but that makes sense!

Possibly the same root cause as to what I reported?

viewtopic.php?f=7&t=118967&p=629845&hil ... th#p629845

The pipe length calculation is incorrect when connecting two separate pipe networks in a corner. Example, make a pipe in a straight line a handful of tiles (length X). At the first blank tile after, start making a separate pipe going perpendicular to the first (length Y). Finally, connect the two ...