next_upgrade target is set to assembling machine 2 by the deep copy. This is causing an error about having a different collision mask.

I've fixed it in my copy by adding: to prototypes/entities.lua

TL;DR Should the confirm button in the about dialog be a back button instead? What ? The confirm button in the about dialog doesn't actually confirm anything. When I went to view the EULA, thanks to a nice little easter egg, I found myself briefly thinking I've changed some option in the about dial...

Yay! I can tell the active provider and requester chests apart. Now if only I could do the same with red, green and copper wires.

Got the same problem here. It will sometimes let one lane through. It looks like it might be that the items on the prioritized output line might be a few pixels out of the splitter, preventing it from detecting them.