Factorio Forums

I use side-loading on underground half-belts (one side of a pair of undergrounds) to create lane balancers. I then place opposite direction these balancers in close proximity. As I design them, they work perfectly fine. However, when I copy/paste the design, some of the underground belts will change direction.

Reproducing it:
If you build it then copy/paste, it tends to break. If you fix this newly pasted copy, it seems to assign direction to the undergrounds, so copies of the copy tend not to be broken. However, if you paste this newly corrected blueprint then copy THAT one, it will break again. My picture includes a properly functioning design and the two possible broken versions.